Despite common misconception software doesn’t intersect with math all that often. Still math skills can be applied to program some very cool stuff.
I had picked rsizr some time ago from post about such math stuff – seam carving at MakeUseOf. rsizr is online service powered by Adobe Flash that allows very advanced tricks with image resizing and rescaling.
What it does
Regular image resizing algorithms rely on recalculating quantity of pixels to preserve (or change) image proportions for whole picture.
Resizing with seam carving works differently – instead of treating all pixels the same it calculates which pixels contribute least to the picture and can be disposed of first.
Since such calculations can be easily tweaked it is also very easy to tweak process into preserving or removing specific parts of images.
Still not magic
There some very impressive demos that show power of such liquid resizing. However it can be tricky to use – even more than regular algorithms.
It largely depends on specific image and what you want changed.
rsizr is nice service that is probably easiest way to play with seam carving. Technique is not mainstream and doesn’t really aim to replace regular resizing but it is powerful way to achieve some effects without need of graphical editor (or skills to use one).