Twitpic is an application that lets you share your photos on Twitter. After setting up an account, you can log in to Twitpic to upload photos from your computer. Twitpic will store the photo on its server, and at the same time will generate a post to your Twitter account with a link to the photo. You can caption and tag your photo, too.
You can also use Twitpic to tweet photos from your mobile phone. The application generates a unique e-mail address based on your username. After taking a picture on your cell phone, just email the photo to that address and it will soon appear in your Twitter feed. The ability to tweet photos on the fly -- as opposed to having to wait to download photos from your camera to your computer -- makes Twitpic and similar applications very popular.
On the Twitpic homepage, a Google world map features recently uploaded photos from all over the world, an interesting way to find Twitter users you might not normally encounter. You can also find Twitpic bundled into some of your favorite Twitter tools, like TweetDeck or Twhirl.