Twitpic is the most popular service for sharing pictures with your twitter followers. If you need an alternative to twitpic look at Pix.im which does the same with few extra features.
Pix.im is a photo sharing service for twitter. With this you can set privacy control like who can see your photos, any one, or just your friends or followers. You can tag your friends in the pictures you upload. It also does some stats like who visited your pic and how many of total views it got. Much like twitter you can see what your friends are uploading and what they are doing on twitter.
Pix.im gives short URL of the picture you uploaded for sharing with your twitter followers. Pix.im is using twitter oAuth for login so no worries while logging to the service. Check out this service if you share pictures often on twitter and you like to have privacy and stats for the same.
Another good application is http://twitsnaps.com. It’s quite easy to share pictures on Twitter, using it.