As you take pictures with the phone and synchronize your phone with the PC, the phone accumulates a photo library. A program running on the phone can access this library in one of two ways:
From the perspective of your program, the PhotoChooserTask is much like the CameraCaptureTask except it takes the user to the photo library and allows the user to choose one photo, which is then returned to the program.
The XNA namespace Microsoft.Xna.Framework.Media has a MediaLibrary and related classes that let a program obtain collections of all the photos stored in the photo library, and present these to the user.
I’m going to show you these two approaches with two programs. Just for variety (and to demonstrate how to use XNA classes ...