The Liquid Rescale plugin is an implementation of the content-aware
resizing by seam carving algorithm by Shai Avidan and Ariel Shamir.

It aims at resizing pictures non uniformly while preserving the
features of the picture, i.e. avoiding distortion of the important
parts of the picture. It can also be used to remove portions of the
picture in a consistent way.

It works both ways, but enlarging gives better results if done in
successive steps. It can use extra layers as masks to select which
features of the image should be preserved and which should be
discarded.

The plugin works on the active layer or floating selection. If a
selection is present, it is saved to a channel. If the layer has a
transparency mask, an option is given to select the behaviour
(apply/discard).