With the Polaroid photos, the characters don't really look dead on at the camera. The photos look like casual mug shots. I think that this look learns towards Sibylle Bergemann effect. The head shots don't reveal anything about their lives and all the audience can do is guess. Also with the way we arrange the photos the audience can guess how the characters are related to eachother.
The 35mm photo have a more relaxed point of view and the photographer her could possible another participant in the group of friends. However this may also pass on the feeling of intrusion to the the audience because they may feel like they are looking at private photos.
The digital photos looked like outsider photos, sort of like still shots from a soap opera. The give the audience insight on the private life of the characters but at the same time create more distance than the 35mm films