Truthers have often said this video is "faked". Osama appears more "chubby" and other "problems" in the minds of truthers.
However, BBC had a show called "Conspiracy files" several years ago. These "conspiracy files" were 1 hour long each and on a specific topic, not only about 9/11. One was about Oklahoma, one about David Kelly etc.. but there was one about Osama and whether he was alive or not (as it had often been claimed that he was dead).
In that program, they included an expert who took a still picture of Osama from a known video of him from 1998 and then they faded from a still picture from the "confession" video to that known picture of him in front of our eyes, and it's a perfect match! See for yourselves:
These clips of this BBC-show are often removed as it's copyright-protected, so maybe this 3-minute clip with the identification of Osama will be removed also, but I wrote the name of the show so you can look it up for yourselves above.
It's as clear as it can be.