we have a tool where people can upload or select image, crop this, so we can print it out on whatever.
but its needing modifications.
only bid if you really understand the relation to pixels in cm and good knowledge of oscommerce principals
modifications is that the input for height and width is synchrone with the crop , pixel warning in image format, javascripterror browser fix, and crop button will show the cropped picture
pm me for the website, so i can show you