Twitpic is a website that allows users to easily post pictures to the Twitter microblogging and social media service.
Twitpic could be used independently of Twitter, in a way similar to Flickr. However several characteristics make this site a companion for Twitter. Twitpic usernames and passwords are the same as the ones in Twitter.
Comments to photographs are sent as a reply tweet. Twitpic URLs are already short, making it unnecessary to use URL shortening.
Anyone with a Twitter account can post pictures to the site. It has about 6.5 million registered users and is an Alexa Top 100 site.
Andrew Warner of Mixergy did a great and detailed interview with him, Check it out!