Head size
The photo must show your entire head, from the top, including hair, to the bottom of your chin. For the photo to be accepted, the head height in the image must be 25-35 mm (1-1-3/8 inches), or occupy 50%-70% of the photo.

USA
Photo requirements
Part of the process of completing and submitting a nonimmigrant visa application is uploading the applicant's photo to the website. The photo must be taken no earlier than 6 months before the day the application is completed. A printed copy of the photo must also be taken to the U.S. embassy or consulate for the interview.

The photo must be taken within the last 6 months. If you are applying for a new visa to replace an expired one, you must have your photo taken again and provide a new photo.
The photo must show your entire head, from the top, including hair, to the bottom of your chin. For the photo to be accepted, the head height in the image must be 25-35 mm (1-1-3/8 inches), or occupy 50%-70% of the photo.
The photo must be square (length equals width), 5x5 cm. Minimum image resolution: 600x600 pixels (height x width). Maximum image resolution: 1200 x 1200 pixels (height x width).
For the best result, the photo background must be white or close to white.
It is very important in the photo. The photo must show the entire face. When taking the photo, look directly at the camera and do not close your eyes.
Color image. Taken within the last six months and matches how you currently look.
Photos of applicants wearing headwear that covers the hair or hairline are not accepted. Exceptions are headwear worn daily for religious reasons.
Clothing that appears in the frame must be everyday clothing. Photos of applicants in uniform are not accepted. An exception is clothing worn daily for religious reasons.
Photos in which the applicant is shown wearing headphones, a wireless headset, or similar devices are not accepted. If you wear a hearing aid or similar devices constantly, you may be photographed with them.
Facial expression must be neutral, eyes open. The face must be fully visible, and headwear must not shade the face.
Do not take photos wearing glasses. As of November 1, 2016, such photos will not be accepted. More detailed information about photo requirements is available here