A straight face is easier to process and distinguish. Since your driver's license photo is used to identify you, the MVC and the police want to reduce fraud or identify theft by making it more difficult to impersonate you. Better facial recognition technology is developing every day, but until then it's recommended that you keep a straight face in your photo.
When you apply for NJ Driver's Permit, you will need to bring the $10 fee, a primary and secondary ID, your Social Security Number and proof of your address. These documents must total 6 points on New Jersey's verification scale. Visit this website for more information about acceptable documents: http://www.nj.gov/mvc/Licenses/DocumentSelector/index.htm.