Take out one stressor of painting - the blank paper.  Using a lightened photo eliminates the hassle of tracing an image and transfering it to your paper and makes for a more accurate starting image to work from that will help you get that important painting just right!  It's also a great way to do a study to practice a work before taking on the final painting.
 
You can choose to use my picture of Parker that goes with my "Parker Freckles" tutorial or for an extra editing fee, I will Photoshop your picture to prepare it for printing, and then send you a lightened photo on watercolor paper of your own choosing.  You can also choose to have me just print out your picture with no edits or changes.  Another option is to choose any of the reference photos I've used in tutorials.  Choose from the menu for the option you want!