I sometimes use the rectangle tool to select the area and copy it to a new file. From there I will try to determine the "size" and adjust my photo accordingly. If the qp is a jpg, then I will make the selected area a new layer, delete what I don't need using the background eraser, and sandwich my photo between the two layers. After that I might play with the rotation of the photo to try and make it fit better.
Credits for Avatar - Dancing Princess Designs: Making Spirits Bright