First of all, I really like the game. There are beautiful pictures and the game becomes more difficult with each level. It's nice.
Just a few suggestions:
- It would be nice to have the saves... It's really sad to lose all progress in one second by pressing the wrong button (Esc).
- Some indicator of how many levels are left until the end of the game (for example, 8/25)
- It would be interesting to have some sort of help (for example, finding 5 correct differences in a row gives you 1 help). This will stimulate the player to look for differences, and not just click randomly.
- And it was already mentioned... the Gallery... Yes, it is really necessary.
It may be a little difficult to implement (I'm not really familiar with programming), so I don't insist... Just suggestions...