Post to Twitter from Flickr (the official way)
If you've been waiting for an official way to post your Flickr photos to Twitter, Flickr has an answer, and may be providing hosting for Twitter users with a new service.
After watching other photo hosts create simple tools for Twitter users to post pictures, Flickr has finally wised up and pushed out its own solution. By divining the popular photo service with access to your Twitter stream, you can now post individual shots there right from Flickr, complete with a fancy Flic.kr shortened URL.
Instead of adding a new button to do this, Flickr users simply set up Twitter as if they were adding another blog to post photos to. Clicking the "blog this" button takes you to a page where you can type in the remaining 116 characters, and see the shortened Flickr URL which is added to the end of the Tweet. You also get a special variation of your Flickr posting e-mail address that directs e-mailed shots directly to your Twitter stream at the same time they're hosted on Flickr.
Flickr still has a ways to go before its a part of third-party Twitter apps. Part of the problem is that most competing services, like YFrog, and TwitPic, don't require users to create accounts. In many cases they simply create them automatically based on Twitter credentials. Flickr, on the other hand, is a service you have to sign up for in order to use. I'm not so sure it would be willing to lift that restriction just for Twitter users, but it would certainly be a great way to woo new ones.