According to the United States Department of State, passport photos must fall between 600 x 600 pixels and 1200 x 1200 pixels. This information is provided for individuals who want to take their passport photos themselves instead of using a professional passport photo service.
The State Department has several other requirements for a passport photo. It must be printed in color on matte or glossy photo quality paper. Its physical size should be 2 x 2 inches. The person must stand facing the camera in front of a white or off-white background. Their expression should be neutral, and both eyes must be open. The photo must be no more than six months old.