One of the excellent programs that comes with KDE is Konqueror. Konqueror is a file manager and a web browser. One of the nicest features of Konqueror is autogeneration of preview thumbnails. This helps a lot when dealing with image repositories and photo albums.
When working with a lot of images, one can notice that Konqueror does not generate preview thumbnails for all of them. This is because it hits the limit on the file size set by default. That is easy to correct though. To fix this, start kcontrol, go to KDE Components where you need to select File Manager in which choose the tab marked as Previews & Meta-Data, where you will find a bar marked Maximum file size. For the images coming out of my Digital Rebel I set a 6.5 MBytes limit and it seems to work nicely.