Somebody who at a big occasion takes photos with everybody they have even the slightest relationship with, so that they can put them up on facebook and make themselves feel popular
Especially keen on the one-on-one shots, and photos with the opposite sex.
Also picture slutted, and picture slutting
Also picture slutface, which is the same except the person concerned looks really ugly or slutty in his or her photos
"Did you see all those photos of Paul on facebook?"
"yeh, he's such a picture slut. he hardly knew any of them"