Maybe the procedure changed now, but check the following link, it may help you.
http://uscis.gov/graphics/formsfee/forms/e-photo.htm
Scheduling an Appointment for Fingerprinting and Photographs
Scheduling An Appointment for Fingerprinting and Photographs for E-Filed Applications
On completion of your E-Filed application, your Confirmation Receipt notice will direct you to call the National Customer Service Center at 1-800-375-5283 (TTY 1-800-767-1833) to schedule an appointment with a USCIS Application Support Center for the collection of a digital photograph, signature, and fingerprint.
You must bring a copy of your E-Filed application, along with a copy of your Confirmation Receipt notice, to your appointment at the Application Support Center.
For these applications, USCIS cannot process your application until you have appeared for your appointment at an Application Support Center. The Application Support Centers listed below are NOT able to collect digital information at this time. You may be directed to another location that may be several hours from your home. Use the list below to help decide if E-Filing will be the best option for you.
Application Support Centers That Do Not Take Digital Biometrics Alternative Application Support Center
Charleston, SC Charlotte, NC
Jackson, MS Memphis, TN
St. Croix, VI St. Thomas, VI
Application Support Centers that are not listed above can collect digital information. See
Application Support Center Locations for a list of all Centers, and to find the location of a Center noted above.