Thanks so much for allowing me to post the above as an answer. As I
said, the two products I've detailed really are some of the best out
there--and free! I've used Gallery myself for a number of years, and
have continually found it to be the best, most full-featured gallery
software around. However, LinPHA has all the advanced search features
you want. In fact, even the commercial gallery programs I found didn't
have the ability to search EXIF tags: only the free LinPHA did!
Again, thanks so much!
Search - mostly via. www.sourceforge.net:
And, of course on Google:
(exif is a file format that allows JPG's to store information on the
'method' used to capture the image. For example aperature, etc..)