Twitter users have image galleries

Twitter launched a gallery for each user with the latest 100 images that he shared in his microblog (starting January 1, 2010) through supported photo hosting sites.

The galleries show photos uploaded both to the recently launched internal photo-hosting of Twitter, and to a number of other photo-hosting sites - yFrog, TwitPic and Instagram.
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Several recent photos of the user can be seen directly in the profile By clicking "show all", you can view the rest of the photos and each photo separately, along with the corresponding tweet.

via Twitter Help Center