A painting of each stage of life must be included in the museum, and those paintings must be portraits to qualify, I had the same question once a long time ago.
I'm having trouble understanding why, since we can use photographs or ice sculptures if we want [and also since I can paint "portraits" of Sims where they're not even in the picture]. Does it affect something? Obviously, tournaments can have whatever rules they want, but I'm really curious about the motivation behind this one.
I'm not going for the hall of fame anyway [I have a dynasty currently running with a cell phone photo museum], so I suppose it doesn't really matter.
EDIT: Ahhh, the photographs and ice sculptures are
in addition to the paintings? Hmm. I've been interpreting that section wrong this whole time.