Hi...
In addition to what Ztcoracat mentioned, you can also try GIMP. Also, since you're running Kubuntu,
digikam is one of the best image editors out there for Linux, from what I understand. If you can find it, Picasa for Linux seems pretty good, too, although it's been unsupported for quite a while now. GIMP, digikam and the ones Ztcoracat listed should all be available in the repositories using Synaptic.
Regards...