(unless they don’t have the storage capacity of maintaining hundreds, if not thousands of images.
The way I see sites getting around that is to have the poster post the image to a sharing site and just link to that. No need to store it then. It is more work for the poster, but takes much less disk space. I can’t see them purging files on a regular basis. That said, they are somehow maintaining a lot of pictures in the Virtual Systems section. Maybe they could use the same mechanism.