The other night the question was raised about tagging and sorting photos. I found http://www.alipr.com this site which, while not being very descriptive on its face, sounds like it can search through your images and put tags on them based on their imagery content. That is, it can tag them as people, architecture, and so forth.

I haven't tried it but there's a write-up on it at http://www.technologyreview.com/read_article.aspx?id=17772&ch=infotech&a=f.

Myself, I don't actually tag my photos, I use the Windows Explorer directory system with a tree of folders and subfolders. I have two main categories, "Art" and "Photo Album." The "Photo Album" folder contains family and other photos while "Art" contains anything I might want to put in my portfolio, enter into competition, and etc. Photo album is generally broken down by year and quarter (it has to do with the file numbering system in my camera). "Art" has subfolders for "Architecture," "Nature," "People," and etc. Each of these has subfolders such as "Animals," "Birds," "Bugs," and etc. So long as I'm diligent about placing images in the right folders it's easy to go back and find what I want and the only expense is the time it takes to file them.

Also, as soon as I download my images from my camera's memory cards I rename them for the year, quarter, and who's camera they came from. For example, a photo taken today with my camera will be converted from IMG_2976.JPG to 093a2976.jpg. This helps me track back to when it was taken and where on my computer it is. It also bypasses the problem of my camera repeating it's numbers every 10,000 photos and the habit of some web-support computers getting hung up on .JPG vs .jpg. I always stay in lower case file names when I'm working with my web site.