Released in 1987, U2's fifth studio album was certified 10 times platinum in the UK and shifted 25 million units globally. Needless to say, copies are far from rare. But if you're lucky enough to own a first pressing of the Irish band's top seller, you're sitting on around $100 (£77).

Identifying a first pressing can be tricky. Many are etched with 'A1' and 'B1' on their respective sides in the area between the label and grooves. But many aren't. In the case of The Joshua Tree, the earliest copies of the album have several distinct characteristics, including several formatting mistakes. These are detailed on online music database and marketplace Discogs, a super-handy resource for identifying first pressings. Internet retailers and collectors' forums can be mines of information too, or you can go old school and get expert advice at your local record shop.

21 classic vinyl albums worth more than you think