Cropping an image succintly
Octave - 59 chars

pkg load image;imwrite(imcrop(imread(input(''))),input(''))


MATLAB - 44 chars (not free, out of the contest)

imwrite(imcrop(imread(input(''))),input(''))


MATLAB seemed spot-on for this. Requires the Image Processing Toolbox (or package image 2.0.0 from Octave Forge). Usage:


Write at prompt 'input-filename' (single quotes included)
MATLAB: Drag from top-left to bottom-right corner and double click the rectangle.
Octave: Click top-left and bottom-right corner
Write 'output-filename' (between single quotes too)