iTag - specialist photo tagging software

There are 3 main standards for including metadata within jpg photo files

• EXIF - used for image capture information (including geolocation), and normally added automatically by the camera (though camera phones and web cams often omit including it)
• IPTC - a standard for adding more textual metadata, describing what the photo actually illustrates, licensing information etc
• XMP - a more recent standard for similar metadata to IPTC

Picasa allows you to give a description to a photo, and to add what it calls keywords (but nearly everyone else calls tags), which are stored in the photo as IPTC.Caption and IPTC.Keywords data.

However there is also a specialist tagging program available in the form of iTag which makes this tagging even easier, and also writes the data as XMP data (in addition to IPTC) for use by other programs that prefer that standard.  This Windows freeware program was written because in the words of it author "I found quite a few IPTC tools but none worked the way I wanted them to. So I decided to write my own."  It is actively maintained and enhanced.

The program's website has a great table which shows the use of IPTC and XMP metadata by a wide range of desktop programs and web applications.