F-Spot is a free open source image manager for Linux.
F-Spot competes against Shotwell. Shotwell displaced F-Spot as the default image manager in both Fedora 14 and Ubuntu 10.10. F-Spot is an alternative to ACDSee for Linux. You might use F-Spot as the next step up from IrfanView when you have a huge number of images.
Classification by keyword
F-Spot and Shotwell let you tag images with keywords for classification. F-Spot lets you add tags as children of other tags while Shotwell has the feature listed on the roadmap for a future release. You could create the tag family then add the names of your family to family. You could then select every image containing a member of your family or photographs for specific family members. If you had Tom as a member of your family, you add only the Tom tag to identify an image as both Tom and family. In Shotwell you have to enter Tom,family to get the same result.