There seems to be a lot of “find the cats hidden in these pictures” games. I’ve played a few recently, but this one is by a different developer, and is one huge picture rather than a series of connected ones (like A Castle Full of Cats). The idea is the same, though.
Not much more to say, really, aside from as well as finding 100 cats, you can also get an achievement for finding 5 gulls. Which I did. It’s free on Steam if you want to play yourself.