KuickShow is a very fast image viewer that lets you easily browse large galleries. A builtin filebrowser and manager is also available. Its usage is somewhat inspired by ACDSee. It supports many file formats, including JPEG, GIF, PNG, PSD, BMP, TIFF, XPM, XBM, XCF, EIM, etc. It can zoom, mirror, rotate images, adjust brightness, contrast, and gamma, and do a slideshow. It is fully configurable through dialogs. It offers a filebrowser with basic filemanager capabilities like renaming, deleting, creating directories, etc.
MRML for KDE is a KDE MRML client which offers integration of content-based queries into Konqueror/KDE. It consists of a KPart (which could be embedded into Konqueror for example) and a kio-slave for communication with the MRML server. You can right-click on an image and choose "Search for similar images..." in the context-menu, which will perform a query on a server and present you a thumbnail view of the results. You can also refine queries by giving relevance feedback.