Sorry, Ara, but the previous posters are correct on this one. You can't do a thing about it, as irritating as it is. The photos are different in execution, and the concept is not something you can own.
I deal with this A LOT. It's incredibly annoying. Some of the imitators have gone to great lengths to duplicate my shots down to the last detail. Frustrating, but that's just the way it goes. On the other hand, I've had entire text pages of mine ripped off, and I mean paragraphs literally cut and pasted without a single word changed. That's a different story, and I can and do take action in those cases.