WP-TwitPic is a project mainly written in PHP, it's free.
WordPress friendly TwitPic class, modified from (http://www.digimantra.com/technology/php/post-pictures-on-twitpic-api-using-php/)
Modified version of http://www.digimantra.com/technology/php/post-pictures-on-twitpic-api-using-php/
Uses the WordPress HTTP request methods instead of cURL directly.