Just ask him to delete it or credit you in some way.
The newbie seems reasonable enough. Stealing? Kid? Harsh. Maybe it was a harmless mistake. We are all using enough copy-written images that, in a way, this is site about ripping off media and recasting it as our own. A movie like "Scary Movie", parody and satire, is itself a form of ripping off someone's work and recasting it as your own. No need to reply or argue with me about, btw. I have no plan to look at your response. Not my business anyways. Just saying you don't bite the newbies. Don't scare off the few liberals that are here.
TL;DR version- If it upsets you that much, just politely ask him to credit you, or, if it's too late, respectfully request him to remove it. Get a lot farther with honey than vinegar. My 2 cents.