Contrary to popular belief, Gimp is not the only image manipulation application for Linux. There are a few.
Today I came across yet another one. digiKam is a KDE-based application for editing and maintaining collections of digital photographs. Iti s possible to store images in albums with comments, tags and dates. SQLite database backend allows for more metadata. digiKam also has a number of image processing features. Basically, it supports KDE image processing architecture and thus can utilize a number of plugins from other applications. The usual suspects for image rotation, levels, curves, cropping, annotating, white balance and color corrections are all there. Check it out.