All the band pictures on Generator came from the Atomic Garden video. They did one take where they were in a small room filled with smoke and Jay got pissed off because he couldn't breathe, so he went next door to an army/navy surplus and bought a gas mask, then used a few frames (notice how all the pictures are movie frames) with it on for the LP. So they didn't really have a photographer; Brett and Jay chose the pictures.
The photos in Stranger Than Fiction, aside from the cover, all were in Discover Magazines in the early 90's. The picture where an old man stares up into a starry night was later on used as an advert for the company Q8.
The picture of the band in The Gray Race was taken in Culver City. Probably the photos of faces in The Gray Race were not taken specifically for the album, but are in fact samples of the work of a particular photographer (Richard Burbridge) whose speciality is such photos.