Photos half a meg each so 2000 per gig. 100k photos might happen, I have a couple of filing cabinets full of 35mm negatives and contact sheets (ok not family snaps).
Put some music and videos in there and you are away.
Half a meg each? Even my cell phone takes 2-3 MB photos. And then if use iPhoto or something, it stores the original and edited photos separately. My humble personal iPhoto library is 65 GB.
Put some music and videos in there and you are away.