Best as I can tell, that is a site where you can upload to your heart's content, and for some of those pictures (I have pretty good internet bandwidth) they are tens of thousands of pixels wide and thousands high. I took that particular panorama and got the 'original' size picture down, and really studied the detail in it until I could almost feel the fog in the distance.
As to copyright, I would contact the photographer before selling his picture, but I have no reservations about looking or show-and-tell. I know some don't even like that but pbase looks to be the supreme forum for those who do.
I talked to a lady last night, just back from Africa, and she had 24 rolls of film (>500 pictures) and was looking for where to post some of them (she got a CD disk for each roll) and I will suggest pbase now.
I think what happens with pictures 'disappearing' is that the server figures out when pictures are being requested, generates small ones on the fly from big ones, and passes the id's of the small ones back. After a pre-determined time, say 10 minutes, it clears them out. That way a person can upload just a huge one, and the server can compress it, then make large/medium/small/thumbnail versions on demand.
Cheers.