#!/usr/bin/env python

from PIL import Image

def seal(im, mark, margin):
    """Adds a watermark to an image."""
    if im.mode != 'RGBA':
        im = im.convert('RGBA')
    # create a transparent layer the size of the image and draw the
    # watermark in that layer.
    layer = Image.new('RGBA', im.size, (0,0,0,0))
    x = im.size[0] - mark.size[0] - margin[0]
    y = im.size[1] - mark.size[1] - margin[1]
    layer.paste(mark, (x, y))
    # composite the watermark with the layer
    return Image.composite(layer, im, layer)

if __name__ == '__main__':
    im = Image.open('sa_sheet.jpg')
    mark = Image.open('seal.png')
    seal(im, mark, (200, 230)).show()