indexing records

What I want to do is figure out a way to index MySQL query results on my PHP site that's not dependent on the id of each record. I've got a MySQL photo database that runs my photo site. Right now, the 'id' field is a sequential, auto-incremented number, and I am using that id as an index for the photos (because it was easy for me to grasp). It works now because the groups are organized in order (for example all the Iran pictures are sequential). But ----------- providing the finest in midget technology