Actually, there are tagging standards for images. Most image cataloging programs don't support them, however.
If you have a digital camera, most likely the software that came with it will allow you to view the EXIF tag and also possibly add IPTC tags. The EXIF tag your camera writes notes the date, shutter speed, and other technical info for each pic. IPTC tag allows you to add captions, headlines, keywords and lots of other info to individual pics.
Of course, for this info to be useful you need a program that is able to read and perform searches. Two programs that I've come across that aren't too bad are Image Walker (
http://www.imagewalker.com/) and PhotoThumb (
http://www.photothumb.com/). Be aware, that the current version of ImageWalker will destroy the EXIF info if you use it to write IPTC info. Photoshop/Photoshop Elements will write IPTC info, I think without destroying EXIF. The free image viewer IrfanView (
http://www.irfanview.com/) will view and write EXIF, IPTC, as well as JPEG Comments. Also, many image editing programs will destroy EXIF/IPTC when you crop the images.
A quick Google search on the terms
IPTC and
EXIF will turn up even more info.
Rob