Currently a bunch of KDE-related stuff is missing in testing ('etch'). I don't know exactly why or when they'll come back but I'd guess they'll return soon... I'd guess they are pushing down new KDE stuff from unstable into testing and thus some dependencies cannot be immediately fulfilled and thus some packages disappear until they have been made to work with the new KDE stuff and there is a time delay for things to drop down into testing.
The
digikam package is currently only available in stable ('sarge') and unstable ('sid').
So for now you'll have to either use the one from testing or the one from unstable. Considering the current KDE stuff is the same in testing and unstable, it shouldn't be an all too traumatic experience to take it from unstable.