Incredibly fun game! I hadn't played something like spot the difference in a long time. Memory games are fun and I think you made something really neat! I also tried the alternate mode a little, and I like the idea of having a manually curated mode and a random mode for players who seek more and perhaps a more difficult challenge.
I do agree with other people about how to play not being quite clear at the start (it wasn't until I read a comment here that it clicked for me), but that's not too hard to address, and the core of the game is very enjoyable.