One more idea for you: Collages. I think pictures with a bunch of pictures in them are really fun puzzles as you have a bunch of people and things going on. Here are the best subreddits I found for that: r/pornscenecollage, r/nsfwpicvideocollages, r/pickheroutfit, and r/onoffcollages. Thank you!!
Also, I think it may be worthwhile to give users the option to turn gifs on or off, so that gifs are automatically excluded from the search if the user chooses it, as those are often blurry as static images for the puzzle. Regardless, I am enjoying this so much, thank you!!!
