While trolling through astrophotos in Flickr, I came across an amazing tool: astrometry.net. It is an automated service that takes a starfield image and returns 'the astrometry world coordinate system—ie, a standards-based description of the (usually nonlinear) transformation between image coordinates and sky coordinates—with absolutely no “false positives” (but maybe some “no answers”). It will do its best, even when the input image has no—or totally incorrect—meta-data.' This means that, without any information about what part of the sky an image has recorded, when or where it was taken, and even if there are artifacts of the imaging system such as optical non-linearities, foreground objects, etc., it will provide a description of the field of view. It also spits out a list of interesting objects that are visible in this field of view.

They've hooked the tool up to a Flickr photo pool. If you submit a photo to the pool, the tool will respond within a day or so by commenting on your image with the world coordinate data and a list of interesting objects. It also puts notes of the correct size on your image for each of the objects.

For examples of the data it returns, check out the notes and comments for these images of Orion and the Antares region that I submitted to the astrometry pool.

I really like the mission of this project—to provide standards-compliant meta data for any astrophoto, including historical ones, so that they can all be searchable and usable in modern science. The core team is composed of people from NYU, University of Toronto, Google, and Microsoft. Awesome project.