What control is used to implement the application screenshot preview in the windows phone marketplace. The control allows zooming , panning and scrolling of images.
This control is also used when scrolling through pictures in the “Pictures” application.
Take a look at this blog post. In it Morten talks about how to achieve what you are looking for. I’ve used this in one of my own apps and it works great
http://sharpgis.net/post/2012/01/17/Building-A-Multi-Touch-Photo-Viewer-Control.aspx