First of all let me say I find it really hard to believe that the repos don't have KIM available as a package. In my opinion, KIM is a must have for KDE if you work with images, even occasionally. Sure, ImageMagick can do it from a terminal, which KIM is just a frontend for, but how many first time Linux users really want to mess around in a terminal to do a simple thing like resizing, compressing, or converting an image. [rant off].
Anyway, open Dolphin -> Settings -> Configure Dolphin -> Services and check mark all the KIM entries.
Hope this helps.