Wikipedia
ExifTool
ExifTool is a free and open-source software program for reading, writing, and manipulating image, audio, and video metadata. It is platform independent, available as both a Perl library (Image::ExifTool) and command-line application. ExifTool is commonly incorporated into different types of digital workflows and supports many types of metadata including Exif, IPTC, XMP, JFIF, GeoTIFF, ICC Profile, Photoshop IRB, FlashPix, AFCP and ID3, as well as the manufacturer-specific metadata formats of many digital cameras.
The image hosting site Flickr uses ExifTool to parse the metadata from uploaded images.