Can visitors filter my posts by what is in the picture?

Yes. Every post's cover is read when it is imported, and the posts page offers an "In the picture" filter built from what was found: with people, posed for camera, landscapes, cities, food, animals, indoors, memes and screenshots, and posters and graphics.

A filter only appears once at least three posts match it, so a visitor never presses one and finds nothing. Nothing needs setting up: covers are read automatically as posts arrive.