I'm too busy for something like this too, but I want to work on this pretty bad because, well, embarrassingly I'm a Catwang user.
I think the 'insert randomly' is a nice feature, but if I were to work on this, I'd focus more on letting users insert their own content. Catwang sells 'Doodle Packs' but I think they're missing a couple of things which your image detection is approaching: the ability to make your own stickers (out of friends, perhaps) and the ability to draw on the image (like Snapchat).
I think the 'insert randomly' is a nice feature, but if I were to work on this, I'd focus more on letting users insert their own content. Catwang sells 'Doodle Packs' but I think they're missing a couple of things which your image detection is approaching: the ability to make your own stickers (out of friends, perhaps) and the ability to draw on the image (like Snapchat).