I don't need to explain it, others have, but since people need explainations shoved in their face instead of doing a simple Google:
http://www.snopes.com/politics/obama/birthers/birthcertificate.asp
"They" would be the guy in the video and all the other morons doing the same thing and saying its a fake, not knowing how scanners work.
FYI, not what happened here, but its possible to fake an entire website.
If you have Windows, try this.
- Start -> Programs -> Notepad (right click and Run As Administrator if on Vista or higher)
- In NotePad, open the file c:\windows\system32\drivers\etc\hosts (no extension)
- Add this line to the bottom of the file.
- 74.125.228.8 www.whitehouse.gov
- Save the hosts file.
- Close any open browser windows, then reopen one.
- Goto www.whitehouse.gov
Everything on the web can be downloaded locally, and you can run a local web server. Using the above trick, anyone can then modify the site and say "hey look what this site did today" in some YT video.