nth-ing that Flickr has been a fairly good photo hosting site for a while now. That said, both Flickr and Tumblr were recently bought by Verizon (which is why Tumblr hasn't been showing the same ads to support net neutrality that they did the last time around), so it is possible that there are changes on the horizon. I pay for Flickr and it has been worthwhile; if you use a free account, they limit your photos to the most recently uploaded 200. Also agreeing that Tumblr isn't a good hosting service for photos outside of its own website (explanation and workaround here on a fanart blog). I wrote a Tutorial about how to post pictures to DoA from Flickr a while back.