This is the way I did

1. Print out the photo requirement page.
2. Take several pictures use your digital camera againt the white background(find a white wall in your house). The pictures should be taken to make sure the size of your head meet the requirement, so you need several from far to near.
3. Get the pictures all print out, and find one meet the requirement the best (put the paper on the back of the pictures, and see ...)