Caption - Open-source captioning tool to help find the right subtitles.
CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
Captioned - Say, show, share. Create a 60 second captioned video.
Dashmote - Dashmote bundles stock image providers to make finding stock images as easy as possible.
Caption This - Create a smart caption for your photo in a second!
Rubric - Generate an instant, cool caption for your photo