At Get Real, Arieanna Foley has some thoughts on Social Networking with Flickr and why people interact more on with photographs on Flickr than with the same photos on a blog:

One crucial difference between blogs and Flickr may be the cornerstone to this mystery. With Flickr, you have the ability to add notes, comments, and tags to photos. On Flickr, you can add a comment to any part of the photo; you can also tag a photo (yours or someone else's) to assign it to that keyword category. Since the tags are searchable, your photos are always coming up and being viewed by others - no matter when you took it. So, people are interacting with the photo in a way not otherwise possible. This creates an ongoing conversation about the photo and the fluidity of its meaning, constantly revising where it belongs in the taxonomy. And, perhaps as importantly, this interaction amongst the Flickr community gives one a sense of contributing to an overall archive of shared experiences.