Eighty images, and the piece count changes what kind of puzzle it is
There are eight categories - Art, Apple, Animal, Car, City, Gradient, Street and Wonder - each holding ten images, for eighty puzzles in total. Every one of them can be solved at 50, 100, 250 or 500 pieces, and that choice matters more than it sounds like it should.
At 50 pieces the shapes and colours in the photo are usually enough to place a piece correctly on sight, so the puzzle is mostly about speed. At 500, individual pieces frequently look like nothing on their own - a patch of similar-toned sky or gravel - and the puzzle becomes a matter of edge-shape matching and process rather than recognising the picture. The Gradient category in particular is worth trying at a high piece count once, since it removes almost all of the visual recognition a photo puzzle normally gives you.
Because the same eighty images sit behind all four piece counts, replaying a puzzle you have already solved at 50 pieces on 500 is a genuinely different experience rather than a repeat.