Imagine (Version: 1.0.8 as of this post) is a full featured image viewer and thumbnail browser. It features rotate, flip, negative and other common effects and filters. Support for plugins and command line parameters as well. It also supports animation creation, a feature less common in image viewers.
Via Tools —> Animation Factory one can create animations. It supports setting delays between frames, setting transparency, resizing the animation, fliping frames horizontally or vertically and even manipulating the colors of the images. It is also possible to extract frames from an existing animation.
Another feature often missing or incomplete in many