It doesn't work. As soon as it hits the first line
imgin = imresize(cropimg,[240,240]);
it will throw an exception because cropimg is undefined. It looks like something written by a very novice MATLAB programmer to find the rows and columns where the image is bright enough to be retained. Instead of all those for loops, they could simply use find(). Then they pad the image with zeros on the left and right and resize it for some reason. Basically they're masking out dark stuff outside the bounding box but doing it in a very odd way. If you want a masking app, just ask me for a demo.
