In season 6's Blood, Kathleen's gift to Elliot of a mirror with "I ❤ daddy" on it was posted in his locker.
I don't know why it took me the longest time to realize that Elliot had pictures of his family on his locker door. Well... I knew, but it never really dawn on me to pause and look until rather recently during this time of writing. The two stand-out pictures of Maureen, her prom date, and Kathy were from season 1's Wanderlust (this episode is from season 7's Fat). As for the other pictures, it's hard to identify of who they are other to assume the other kids and unknown elderly lady.