Art can be worth millions if you have a genuine masterpiece on your hands. However, proving the authenticity of a piece that is centuries old can be a huge challenge, particularly if it's not clear whether it's the real deal.

Read on to find out which iconic pieces of valuable art might be fakes – or could be worth a fortune. All dollar amounts in US dollars.

The 17th-century artist Rembrandt has produced some of the world’s most valuable and well-known paintings.

In 2015, two of his portraits sold for a record-breaking $180 million (£138m) at auction, while one of his self-portraits sold for $18.7 million (£15m) in 2020.

The Polish Rider, a painting famed for its haunting and intriguing qualities, was beloved by many fans of the Dutch artist's work – until experts suggested it might be a fake.

In 1969, a group called the Rembrandt Research Project began examining The Polish Rider, among other pieces.

Group members Bob Haak and Josua Bruyn came to the conclusion that the canvas, which is believed to date back to the 1650s, hadn't been painted by the Old Master himself.

The painting's lack of visual balance, seemingly unfinished background, and inauthentic brushstrokes were all cited as reasons to believe it hadn't been painted by Rembrandt but by one of his pupils – possibly a young man named Willem Drost.

The Frick Collection in New York has owned the painting since 1910, when it purchased it for $408,000.

On its website, the gallery acknowledges that another artist might have been involved in the creation of The Polish Rider, suggesting that the painting "may have been an unfinished composition, brought rapidly to completion by Rembrandt – or another artist – so that the work might be included in one of the artist's bankruptcy sales".

With widespread agreement that at least one other person was involved in the creation of The Polish Rider, questions of authenticity continue to cast a looming shadow over the value of the piece today.

Las Meninas, Diego Velázquez's 1656 portrait of the Infanta Margaret Theresa surrounded by her maids of honour, is the main attraction in Madrid’s Museo del Prado art museum.

The artist’s use of mirrors and strange angles leaves the piece wide open to interpretation, resulting in it becoming one of the most celebrated and studied paintings in the world.

However, it's a smaller draft of Las Meninas that has caused the biggest arguments, with ongoing questions as to who painted it.

Purchased in the early 19th century by the British politician William Bankes to displaying in his Dorset country house Kingston Lacy, there are significant differences between the original and the more diminutive version. Experts were quick to question whether it was a first draft by Velázquez (pictured here) or, in fact, a copy.

Some notable specialists believe that the version that Bankes acquired was simply a first draft, painted by Velázquez to be approved by King Philip IV of Spain, the father of the Infanta Margaret Theresa.

However, most experts maintain that it's actually a copy by Velázquez's son-in-law and student Juan Bautista Martínez del Mazo, which renders the painting's worth unknown.

A compelling art war has centred around Red, Black & Silver, which is attributed to the renowned artist Jackson Pollock.

Pollock may or may not have created the painting shortly before his untimely death, and the topic was hotly debated by Ruth Kligman, his former lover, and his widow Lee Krasner. 

Kligman’s side of the story is that Pollock painted it for her a few months before his death in August 1956.

Yet Krasner, who played a key role in the Krasner-Pollock Authentication board, refused to authenticate it, believing it to be a fake.

Authorities denounced the painting as showing no characteristics of authentic works by Pollock, and an expert panel rejected it as a fake.

Kligman was adamant it was a genuine Pollock though, and even took and passed a lie detector test in a bid to prove it.

Forensic testing completed by Kligman’s estate after her death in 2010 tells a different story about the painting's true authenticity.

In 2013, a forensic scientist who was testing the painting found traces of polar bear fur from Pollock’s rug. Some of Pollock's own hair and particles from his home were also found, suggesting it was the real deal.

Given that Pollock’s Number 17A sold for $200 million (£154m) in 2017, the eventual decision surrounding the authenticity of Red, Black & Silver will make a massive difference to its value.

With replicas such as the one shown here made and exhibited around the world, the Nefertiti bust is one of the most recognisable and loved archaeological discoveries of all time.

Nefertiti was married to the Egyptian pharaoh Akhenaten, and the bust depicting her is widely believed to have been crafted by royal sculptor Thutmose in the 13th century BC.

Until recently, the "original" 3,400-year-old artefact was believed to have been discovered by archaeologist Ludwig Borchardt in Egypt in 1912. 

Now exhibited in Berlin’s Neues Museum (pictured), the iconic bust has caused its share of controversy over the years.

Despite many requests from Egypt, Germany has so far refused to give the treasure back, enjoying the millions of visitors it draws each year. However, scandal engulfed the statue in 2009 when two art historians challenged its history.

The experts argued that the bust could be a fake, pointing out that, while it's possible to carbon date the pigments, which have been proven to be Ancient Egyptian, the bust itself can’t be accurately dated as it's made of plaster-covered stone.

With no concrete evidence of the artist behind the canvas, the fame and fortune of the Chandos portrait, which was painted in the early 17th century, centres fully on the person it supposedly depicts.

However, experts are only reasonably sure that it's actually playwright William Shakespeare in the painting...

If it is a real portrait of Shakespeare, painted in person, the National Portrait Gallery could be the owners of the only accurate likeness of Britain’s best-known cultural icon. Other portraits of the Bard have been found to be fakes or dismissed due to a lack of evidence.

The National Portrait Gallery exhibited the Chandos portrait, along with five other works of art that were once believed to depict Shakespeare, in its Searching for Shakespeare exhibition in 2006. 

While experts at the gallery have admitted they can’t be completely sure if this is the true face of Shakespeare or not, three-and-a-half years of research has concluded that the painting dates from the correct period.

The study also found that the sitter is the right age to potentially be the playwright, and that his attire reflects what writers in Shakespeare’s day would have worn.

In 1994, art expert Marina Zagidulina was working to identify antiques at the Russian border when she came across Man with a Shovel, a painting which she immediately identified to be by the Russian artist Kazimir Malevich. 

Malevich is best known for his Black Square painting (shown here) and his works can sell for millions at auction. 

However, there are numerous factors that cast doubt over whether the painting Zagidulina found is a genuine Malevich or not.

For one thing, it looks as if it has been touched up with fresh paint and the thickness of paint in the middle of the canvas varies.

It's also been considered suspicious that the artwork was discovered in the 1990s. Around that time, many forgeries were sent to the West by the Soviet Union as it disintegrated. 

Yet art historians don't agree. According to art expert Olesya Inozemtseva, the use of colour and application of paint both suggest that the artwork was created either by Malevich himself or by one of his students.

Until the painting is authenticated, the debate continues...

Another debate that's still raging on surrounds the purchase of The Madonna of the Pinks by London’s National Gallery. The institution paid £22 million ($26m), half of which was public money, for the unique slice of art history. But is it a fake?

With Raphael’s drawings (such as The School of Athens, shown here) comfortably selling for tens of millions of dollars, the gallery has made an excellent investment if The Madonna of the Pinks is found to be a genuine artwork by the High Renaissance painter.

Having already been denounced as a fake, the tiny painting was hung in a corridor of Alnwick Castle in England, where it was discovered by art historian Nicholas Penny in 1991.

However, in February 2004, the National Gallery decided to buy the painting.

Nicholas Penny, who would later serve as the director of the National Gallery from 2008 to 2015, believed the picture contained crucial clues that proved it was the genuine article and not a copy.

Testing backs this up. However, with over 50 existing copies of this composition, and with no signature, date, or mention of the painting in any 16th-century documents, critics remain unconvinced.

Leonardo da Vinci's Mona Lisa is arguably the most famous painting in the world.

While there's no doubt about the authenticity of the masterpiece that's on display in the Louvre museum in Paris, some experts are confident that it has a twin – a second, similar portrait that was painted by the Italian artist.

In 2012, a Swiss non-profit organisation called the Mona Lisa Foundation presented a second portrait of the Mona Lisa to much fanfare, claiming it was an earlier version that da Vinci had left unfinished.

They said the painting had hung in an English manor house for more than a century before being moved into the London apartment of art dealer Henry Pulitzer in the 1960s. It was later stored in a bank vault until 2008.

The foundation carried out an array of scientific tests and research to back up its assertion about the painting's origins. But not every expert agrees.

Martin Kemp, emeritus professor of art history at the University of Oxford, for example, thinks the claim is unlikely. While infrared examination had shown that the Louvre Mona Lisa underwent an evolution, the earlier Mona Lisa seemed too exact, he told the BBC.

Luke Syson, director of the Fitzwilliam Museum in Cambridge, agrees, regarding the artwork as a copy. 

There has also been controversy over who actually owns the earlier Mona Lisa.

The Mona Lisa Foundation says the painting belongs to an international consortium, while a London-based couple, Andrew and Karen Gilbert, contacted the foundation in 2012, claiming that they owned 25% of it. They said they had inherited the share after an ancestor bought a quarter of the painting from Pulitzer in 1964 before it went to the bank vault.

The debates surrounding the painting’s authenticity and ownership continue...

When this mysterious painting was found under an old mattress in an attic in Toulouse, France in 2014, art historians heralded it as one of the most important artworks to emerge in modern times, believing it to be a long-lost masterpiece by Caravaggio.

However, there are doubts about whether or not the Italian master really painted it.

Although Judith Beheading Holofernes was authenticated by French art expert Eric Turquin, several specialists believe it is a copy made by the Flemish artist Louis Finson, who worked alongside Caravaggio.

But Turquin insists it's the original from 1606, even more so after the canvas was cleaned in January 2019, a process that took three weeks.

Despite the controversy, there was proof enough that the painting is a Caravaggio for J. Tomilson Hill, the billionaire hedge fund manager who purchased it in June 2019.

Hill acquired the painting, which was expected to sell for $178 million (£138m), for an undisclosed sum just two days before it was due to go to auction in France. Interestingly, there was no set minimum price on the artwork.

The new owner, who sits on the board of the Metropolitan Museum of Art in New York, is reportedly planning to display the painting in a museum.

In 2017, history was made when da Vinci's Salvator Mundi sold for a record-breaking $450 million (£346m) at Christie’s New York, making it the most expensive art sale of all time.

The painting, previously owned by the Russian billionaire Dmitry Rybolovlev, was reportedly bought by the Abu Dhabi Department of Culture & Tourism to go on display at the Louvre Abu Dhabi. However, experts have cast doubts about its authenticity...

At the time of its sale, Salvator Mundi was declared to be an authentic da Vinci work, having long been dismissed as a copy by a student of the artist.

In recent years, however, a handful of art historians, da Vinci scholars, and critics have suggested that the piece might actually be the creation of the artist’s studio assistant Bernardino Luini, whose work typically sells for less than $1 million (£768k).

In February 2019, renowned art historian Jacques Franck told the Sunday Telegraph that staff at the Louvre Paris believe it's not a true da Vinci. He also wrote to French President Emmanuel Macron, urging him to stop the artwork from being featured in a da Vinci exhibition at the Louvre.

In April 2021, a French documentary titled The Savior For Sale revealed that Louvre officials had doubted the work's provenance and, following examination of the painting, believed that da Vinci only contributed towards it.

This revelation came shortly after the compilation of an official yet undistributed book about the painting was prepared (reportedly "in case the Louvre got the chance to present the painting", according to The Art Newspaper) by the Louvre in 2019, attributing the work to the master. However, as the Louvre does not own the painting, it will neither confirm nor speculate on any findings.

Another art historian, Frank Zöllner, explains that the painting, which was badly damaged, had to undergo extensive restoration, making it difficult to assess the original quality of the work.

Discussing Salvator Mundi in the preface to his 2017 book Leonardo – the Complete Paintings and Drawings, Zöllner notes that the painting's "strongly developed sfumato technique" corresponds more closely to Bernadino Luini than the style of da Vinci himself.

Further complicating matters is the fact that the painting hasn't actually been seen since it was sold in 2017.

In October 2019, it didn't appear in a Louvre exhibition of da Vinci's work, despite the museum's requests to borrow it. The painting is also at the heart of an ongoing dispute between the 2017 seller Dmitry Rybolovlev and Swiss art dealer Yves Bouvier, who originally sold the painting to the Russian in 2013.

Rybolovlev claims that he has been swindled out of $1 billion through the purchase of 38 expensive artworks bought over the last decade, while Bouvier recently told CNN that he is preparing his own multibillion-dollar counter lawsuit against Rybolovlev.

In 2021, the Prado Museum in Madrid listed it among "attributed works, workshop or authorised and supervised by Leonardo" in a catalogue for a da Vinci exhibition. The confusion and controversy surrounding this piece is seemingly never-ending…

Purchased by the UK's National Gallery in the 1820s, The Triumph of Silenus was thought to be one of three bacchanalian scenes painted by French artist Nicolas Poussin for French minister Cardinal de Richelieu.

By the 20th century, however, doubt was cast over the authenticity of the painting by scholars, with its uneven finish and the fact that some of the figures are "coarsely executed" causing concern. 

By the 1940s, it was widely considered to be a copy and was relegated to storerooms as a mere imitation "after Nicolas Poussin".

However, new research has found it could be the real deal.

Conservation work on the painting, plus further technical analysis that showed the composition of the paints and the canvas weave to be the same as two other bacchanalian paintings by Poussin, have resulted in the National Gallery now labelling the work as a real Poussin.

All three paintings were displayed in the National Gallery’s exhibition Poussin and the Dance, which ran from October 2021 to January 2022.

Rock star Alice Cooper had forgotten he owned this haunting Andy Warhol silkscreen until he rediscovered it in storage in Arizona in 2013.

The iconic Little Electric Chair had been rolled up in a tube among some of Cooper’s touring artefacts – including his own electric chair, which had featured in his dramatic live performances in the 1970s – for around four decades.

Cooper was reportedly a big fan of Warhol, with the artist's work said to have inspired the electric chair element of Cooper's shows.

Cooper had been encouraged to find the artwork after his manager Shep Gordon heard how much money Andy Warhol’s work typically fetches at auction.

Reluctant to display something that could be of huge value in his home, Cooper put the silkscreen back into storage until he announced that it would be going up for sale.

The 22-by-28-inch piece had an estimate of between $2.5 million and $4.5 million (£1.8m-£3.2m) but it didn't sell. One potential reason for that is that there are some serious doubts about the artwork’s authenticity…

There's some scepticism as to whether Cooper’s silkscreen is a real Warhol, as it lacks the artist’s signature.

Cooper commissioned art dealer Richard Polsky to authenticate the piece. Polsky, who is a Warhol expert, believes it was created in either 1964 or 1965, which would match the dates of Warhol’s Death and Disaster collection that featured the electric chair image.

Typically an artist’s estate would review artwork before it goes to auction but the Andy Warhol Foundation dissolved its authentication board in 2012 following price-rigging allegations. 

In November 2022, the Escher in the Palace museum (pictured) in Den Haag (The Hague) in the Netherlands put a long-concealed self-portrait of Rembrandt on display.

It's the first time that the painting has been exhibited since 1967. Part of the momentous occasion related to a recently published book by art historian Gary Schwartz, who argued that the painting is actually a self-portrait – despite claims suggesting otherwise.

But whether or not Rembrandt created the painting is only the tip of the iceberg when it comes to this masterpiece's storied past over the last 200 years...

The museum has traced the ownership of the painting back to 1823, when the future King Willem II of the Netherlands purchased it in Brussels.

Although the king's art collection went to auction after his death, the Rembrandt in question stayed in the Netherlands for most of the 19th century. From there, the painting travelled to Germany with a grand duchess, before being stolen from the Weimar Museum in 1921. 

The story then fast-forwards to 1934. Leo Ernst, a plumber from Ohio, claimed that he'd woken up after a night of drinking with German sailors in New York minus his money but in possession of three paintings. Embarrassed that he'd been scammed, Ernst hid the artworks away.

Ernst's story only came to light in 1945 when his wife Anna Cunningham took Rembrandt in a Red Beret to a local museum, where it was identified as the long-lost self-portrait. Suspecting the painting had actually been stolen during World War II, the US government seized it, eventually sending it back to Germany in 1967.

Art historian Gary Schwartz (pictured) points out that between 1823 and 1969 there was no doubt that the portrait had been painted by Rembrandt himself. However, modern scholars and historians are undecided if it may have been created by a pupil instead, potentially Ferdinand Bol.

While Schwartz and the Escher Museum highlight that doubts have been fuelled by damage sustained during the theft and disappearance, both believe in the portrait's legitimacy. Others are less convinced, however. One expert told the New York Times that, after viewing the portrait in The Hague, he still couldn't attribute it to Rembrandt for stylistic reasons. 

The painting's current owner actually commissioned Schwartz to write the book about the painting. While the author, who specialises in Rembrandt, says he's uncertain if the owner ever plans to sell it, he does admit that authenticating the piece as a self-portrait would significantly increase its value.

An anonymous art collector bought an oil painting titled Standing Male Nude in 1997 at an auction in Geneva following the previous owner's death.

Sold as a self-portrait by the German-born British painter Lucian Freud, grandson of Sigmund Freud, it depicts a naked man from the back, partially bent over, in a less than flattering pose. The Swiss collector paid around $70,000 (£58,000) and added the painting in his collection. 

In 2002, he decided to a little reconnaissance work about the piece, which appeared to be unfinished. He listed it on eBay, along with his phone number. In doing this, he says his intentions were not to sell but to simply collect information.

The strategy worked, although not as he might have expected. Freud himself called the collector, saying that the painting belonged to him and demanding that he sell it back.

The collector declined and recalls that Freud called again a few days later, offering to double the purchase price. When the collector turned down this second offer, he claims Freud told him he will "not sell the painting all your life".

Following the phone altercation, Freud and his estate refused to authenticate the painting for the next 20 years.

Working with art experts across Europe, the Swiss collector sought to prove the painting’s origins, even hiring a private investigator, as he believed the painting could be worth a fortune if authenticated. In 2012, for example, a self-portrait of Freud with a black eye (pictured) sold at auction for £2.8 million ($3m).

Finally, in November 2021, scientific tests involving pigment samples and AI technology revealed definitive proof that Freud had painted the self-portrait. The owner and his investigator speculate that Freud, who passed away in 2011, had simply been embarrassed by it. 

Now take a look at the world's most valuable paintings