Derrick Barry has been an impersonator of Britney Spears for a long time. He entered his act into America's Got Talent: Episode 301.
Derrick looked like Britney Spears. He imitated her singing too. He was one of the better impersonators of Britney Spears. The judges, comprising of Piers Morgan, Sharon Osbourne and David Hasselhoff, were impressed by him. They gave him the chance to move on to Las Vegas.
This season, America's Got Talent offers $1 million in prize money and a gig in a Las Vegas entertainment spot. The winner has to perform his/her act and make it into an entire show in Las Vegas. The winner in 2007 was Terry Fator. He had a $100 million deal to perform in Las Vegas.
Source: youtube video.