@alt_text_bot is an open source Twitter bot that provides description of an image included in a tweet that mentions it. From the author’s description:

Twitter is an important part of public discourse. As it becomes more and more image heavy, people who are blind are left out of the conversation. That’s where Alt-Bot comes in. Alt-Bot fills the gaps in image content using an image recognition API to add text descriptions.

The bot uses the CloudSight API for image recognition. Before using @alt_text_bot, you need to sign up at alttextbot.com — this is due to problems with spam in the past.

The bot was created by Cameron Cundiff.