Digital Photo Management In Linux, Part 1 - page 3
Mac Envy? Hardly...That's all the basic, easy stuff. Now it gets interesting, because as anyone with giant photo archives knows, cataloguing and finding the darn things is the hard part. Digikam has two good tools for managing your photos: tags and albums.
Albums are the individual directories that you create for your photos. Each album, like any directory, can have sub-directories. You can organize albums together with the Collection tag; right-click on any album and select "Edit Album Properties". Then find all the albums in a Collection with "Tools -> Advanced Search".
Tagging is the power tool for picking out specific photos from your vast collection. Right-click any thumbnail or image and select "Assign Tag." You can assign multiple tags to a single photo, which is handy when your photos fit in multiple categories. For example, a beautiful mountain landscape could be tagged as "mountain, sky, forest". Then use "Tools -> Advanced Search" to find photos by their tags. After you create a new tag, Digikam automatically puts it into a drop-down list.