Start by looking at the large side, there is a lot to learn here. Easy to se quickly is the 'rib' down the back. Some AK47 magazines have a raised seam where two sides are welded together, I assume to add strength. Chinese AK47 magazines however do not have the seam. (yellow arrow) Other things to compare are the face where the magazine touches the magazine well of the rifle (red arrow) the number and quality of the stamping of the raised ridges down the magazine face (blue oval), the shape of the mag catch (blue arrow) and the weld spot visible on some but not others (orange oval)

A few more pictures of the top and bottom of these AK47 magazines. Note there are lots of things to compare on these three samples

Looking down the back of these three types of AK47 magazine it's easy to see many differences between them. These are NOT AK47 clips.. a clip is a strip of metal that holds the rounds (bullets) with out a spring (usually) these are technically called an Ak47 box magazine (as opposed to a drum magazine) And looking at these it's obvious they are really just curved metal 'boxes' to hold ammo

Looking closer at the mag catch on these three AK47 magazines the minor differences are more apparent. the magazine on the left is a Yugoslavian 'bolt hold open' AK47 (7.62x39) magazine and the follower is an obvious way to tell this magazine apart from the others. The Yugo AK47 mag are the only type with this style follower which look different, and also are what keep the bolt stay back in most AK47s (the bolt does not usually stay back) The white arrow points to the followers, the one on the left is the Yugo bolt hold open mag. The lack of a rib on the magazine on the right is a sure sign that it is a Chinese AK47 mag, and it's unique mag catch is totally different from most European Ak47 magazines (red arrow)

The 'bottom' of the AK47 magazines usually can tell a collector the most information quickly. The patterns, shapes and finish are easily apparent from this end. Things to look for include the loaded indicator hole shape (red arrow), rivet patterns (orange oval), the rib, or lack of rib (blue arrow), ridges around base of magazine (green arrow) and the floorplate (yellow arrow)