If you don't know which cemetery to locate the grave, then a photo request will not help. You have to be able to make the request via the cemetery page. Use the search engine or the Cemetery Map to locate the cemetery where you think the person is buried.
Go the the Cemetery page for the cemetery where you are pretty sure the person is buried. Scroll down and you will see a place to enter a photo request. You must be very specific for the name or any relatives that might also be buried there, and if you know a plot or family plot, about where the burial is located give that information as well.
And if may be some time before (if ever) your request is filled, if no one is actively working on photographing in that cemetery or that town. Sometimes you get lucky and connect with a photographer who is working through a bunch of local cemeteries and is willing to go out there to take the photo for you.
If that should happen be sure to send the person a thankyou note!