I've come across a bug:
Somehow, the program can't process this one image: http://www.mediafire.com/?6lkon7iws6yw611
Also, I have a suggestion, if I may.
Although removing the white space is useful, I'd like to be able to keep the canvas at the same dimensions (in my case 824x1200). The reason is that when refreshing the screen (when changing pages) the Kindle will only refresh the space that the new image occupies. For instance if the current image is 824x1200 and the next one is 800x1200, there will be 12 pixels on the left and the right that will not refresh. Thus displaying a messed up page.
I'm guessing the easiest would be to change the canvas size after the cropping.
No big deal though, since I can batch-resize the canvas in paint shop pro afterwards.
Thanks for your work.