Seems like it is no easy way to display all the media files under a
wikimedia category -- for example if someone wants a picture of a
library, he or she will need to go into each sub-category under
"Libraries":
http://commons.wikimedia.org/wiki/Category:Libraries
While Wikimedia is not yet the most popular stock photo source, IMO
having this flattening functionality would be useful to those who are
looking for stock photos.
Rayson