This blog post: 30+ Powerful Ways To Share Images on Twitter has (30) sites, most of which have a great interface with Twitter that might include a profile where users have backlinks that'll be picked up by search engines. Thirty options is too much for regular use, but even irregular users would have backlinks. I recently started using Posterous because they host images in a blog environment, and like Tumblr have a community where you can start finding like-minded people. Posterous also integrates a wide variety of services. I chose to connect with Twitter, Facebook and Blogger. I can e-mail in an image with description that will post to my Posterous blog, then within moments the same post shows up on this Blogger account, as well as a link (with visual) on my Facebook wall, as well as a tweet on Twitter linking back to the Posterous post.