That's a Rainford's Butterflyfish I believe - Chaetodon rainfordi
Although that particular one in that photo looks like it's been modified - perhaps dyed. The physical features are clear for a Rainford's, but the banding is much too dark and looks mottled - blended with the yellows. Where the brown is, it should be lighter, speckled even with brown, not solid like that, and there should be thick and distinct yellow bands on both sides of the brown. That one is either a very rare color varient, or has been messed with.