I've seen in other forums that the passport photo required by the visa can be the larger 2x2inch format (with a stark white background) for the US if the application was completed in the US. This is opposed to the the U.K. Standard of 35x45mm on a cream or light grey background. This was in 2009 posts, and the guide to supporting documents on the U.K. Government website takes you to their passport photo info.