A simple explanation
You must remember that in Islamic societies many engraved images (or drawn) are banned. As a result, they probably don't have many trained cartoonists. They probably used the picture because it did resemble their former leader, and since they didn't have a cartoonist of their own, they "borrowed" the picture.
It was an opposition newspaper, so the image of the "Ayatollah" being squished by a giant thumb was used to stir up trouble.