Agreed, US visa apps require a different size picture to the standard format one expects in Europe (slightly larger/squarer).
Be cautious if getting a visa from there and relying on the photo-booth at the embassy on the day itself. If it were to be out of order, after having waited say three weeks for your appointment, you're stuffed (as I witnessed the day I went into the US embassy in London a couple of years back).
There is a photo-booth right in front of the gates exit of Toa Payoh MRT. I had to get a passport picture for a Vn visa, went there on my last evening, and it was out of order. Went to Novena and Velocity where I was sure I'd seen others... no photo-booths. Went home, photographed myself against the background of a white wall with my wifes camera, downloaded it, bit of photo paper, set the print format... job done <phew