This is a little utility I'm trying to use to automagically rotate and crop the black borders off of pages straight from my scanner. It works decently for clean pages with lots of white around the edges but breaks down when there's a lot of ink that goes straight up to the edge. It does not transform the image, but rather produces a transformation plan that, if followed, will probably straighten and crop it decently.
There are probably countless improvements and optimizations to be made. The former will come with time; the latter does not matter much as the time taken to analyze is much less than the actual time it takes to shell out to ImageMagick or GraphicsMagick for the actual transformation.
It is presented as a package; a standalone tool can be found in /autocrop/main.go. For now it just takes a single image argument (and some optional flags) and returns the ImageMagick command line string needed to process the image.