Cordy explained photographs. While you cannot see vampires in the camera their photograph is taken because the only mirrors used as so that you can see the picture, when you take a photograph the shutter opens and burns the light onto the negative, thus no mirrors (okay I added my photography knowledge to that). For Cordy's explaination on why vampires can photograph, just not well, see "Are you now or have you ever been?"
I think it was meant to be explained in the pilot that the reason clothes don't go are because of the vampire's essence (which I guess surrounds them) is killed and the clothes are part of that. The real reason is because it'd be awkard to keep leaving dusty clothes around but thats the Buffyverse reason.