I read this article on tagging and am in love with the idea of tiered tags as an efficient way to apply multiple, related tags. Being a cheapskate and photography amateur at best am looking for the free path to do this. I'm afraid Picassa does not support this feature. Has anyone that uses digikam or itag seen this feature? Is it available anywhere else?
There are plenty of software that do this and they start quite cheap to. The feature you are looking for is called hierachical keywords or categories, depending on the software.
From my DAM software comparison, there is PicaJet FX, IMatch and ID Imager. They each do things and perform differently, so knowing something other than they support categories is important too.
Our Daminion (PicaJet v3) supports hierarchical tags that have been written in Lightroom. (as well as many other tags like rating, color, title, etc...).
Tags can be organized with no limitations on nesting depth. The program automatically updates the file metadata after any tag changes.
PS. I am from Daminion Software team (former PicaJet.com).