It's true that websites and sofas have different refresh rates, but I'm guessing you didn't read the OP, check out the site in question, or click through to any of the examples he provided.
If you do, you'll see that we're not talking about general conventions here (e.g. the similar layouts of YouTube and Kickstarter pages). Nor is this "emulation" in many cases. It's just unvarnished theft (i.e. using the same copyright protected photos as backgrounds).
Best thing to do is to send the owner a Cease & Desist letter, and if they're based in the US, a threat to have the site pulled by the webhost under the DMCA in the event that the owner refuses to comply. It's diplomatic to give the owner a way to save face be acknowledging that that may also be getting victimized by an unscrupulous third party who is passing off the work of others as their own. But also note that this doesn't change the facts of the matter, and state that, one way or another, the site must come down immediately.
You shouldn't say or offer anything else until they call you back and offer you a chance to gauge their demeanor. Chances are good, they're going to be angry. Question is, at who? If it's with you (for ruining their day) then fuck 'em. They're not the kind of people you want anything to do with. Just tell them they have 24 hours to comply or you'll have the site pulled for violating copyrights, and that you won't release the claim unless they pay you several thousand dollars. However, if they're reasonable, they'll be angry with their vendor, apologetic with you, and then you can turn the exchange into a sales call.