XMP Lowdown

The Extensible Metadata Platform (XMP) is a specification describing RDF-based data and storage models for metadata about documents in any format. The specification includes information about embedding XMP in text files such as HTML and SVG/XML; image formats such as JPEG, TIFF, and GIF; and Adobe formats such as Illustrator, Photoshop, and Acrobat files. While its use of the RDF metadata format comes with some caveats, RDF enthusiasts should be pleased to see that the company making the most popular image manipulation tools has made those tools capable of reading and writing RDF metadata about these images.

http://www.xml.com/pub/a/2004/09/22/xmp.html