Witch doctors are actual people who exist and act as healers/shamens in their tribes. The symbolism of Obama as a witch doctor can simply be construed as Obama wanting to play the role of a mystical healer, which is what he's doing in reality, in a sense.
The fact that witch doctors and Obama are both black are unavoidable, because they are both black in reality. One can portray Obama as a witch doctor in order to symbolize his role as a mystical healer without necessarily be alluding to black people as savages.
Then again, there is a very good chance that the person who made that image IS a racist. I'd put my money on it. But you can't determine that from the image alone.
