I sometimes find it helpful to state the obvious ....

One of the major values of Flickr is that it is a low-entry mechanism for making photos 'citable'.

You can give them a URI, a handle, that can be copied and exchanged, and which makes it that much easier for them to enter the shared network space.

The ability to copy and share a URL for most pages is one of the ways in which Technorati, Google or Amazon differs from earlier generations of services.