Although there are many image viewers for Linux, most of them are GTK-based and KDE is left behind with not so many options. Of course, there are applications like Krita or Kolourpaint, but these are image editors, not just simple viewers. Gwenview is the default image viewer in KDE, and it does its job very well. Not only it has enough features to accommodate the more demanding users (like ratings, file browser or thumbnail view), but its functionality can be extended using the KIPI plugins, a KDE set of image plugins used by applications like DigiKam as well, besides Gwenview.
