Don't worry, the photo that everyone had hanging up in their university dorm isn't a fake. This iconic image is one of the most famous of photographer Neil Liefer's career, and its prominence stands testament to the impact Muhammad Ali still has on popular culture. The part that everyone gets wrong is the description. From history books to newspapers, the photo is almost always accompanied by a title along the lines of "Muhammad Ali knocks out Cleveland Williams at the Astrodome, 1966."
The date is correct. The people involved are correct. It wasn't a knockout though. The referee never counted out Cleveland Williams. He was knocked down by Ali just moments before the second round bell was sounded, and Williams was helped back up by his corner men and continued to fight.
Ali's victory didn't come until the third round, after Williams was knocked down once again, then struggled for a short while longer until referee Harry Kessler stopped the fight.