It’s done with Photoshop
Here’s the first image I came across. It shows Obama holding a sign saying “Islam will dominate the world.”
It’s an obvious paste-up job. Note that the light comes from the left on the hands, but from the right on the face. Obama’s head has a white seam around it too. The facial image seems to be higher resolution than the hands.
Here’s the original.
The next one has a bit better quality.
But it is obviously derived with a little help from an original photo of Osama Bin Laden and a computer paint program.
So that is how one converts Obama to Islam.