There are three things wrong with this image. One is obvious. Can you see the two others?
The first step is to remove the sky from our target image.
Next we remove the volcano:
And we composite the two together:
Next we cheat a bit and place the original image back in as the sky (with a offset) + some of Photoshop touchup
Finally, we cut out Obama and place him somewhere inconspicuous + plus some Photoshop patch tool magic.