To extend the share menu to include your photo share application, create a new file called E0F0E49A-3EB1-4970-B780-45DA41EC7C28.xml in the root directory of your main project. Rather than typing the name by hand, you may prefer to copy the XML file to your project from the downloadable sample code.
Using the Visual Studio Properties window, make sure that the XML file build action is set to Content. Set the Copy to Output Directory option to Do Not Copy.
The existence of this file in the root of your XAP file indicates to the phone OS that your app participates as a Share application.
The awkwardly named XML file uses a GUID in its name. This appears to be an attempt to avoid collisions with other filenames. ...