There are two ways to do this. The easy way (implement this free dll called EZ_iso) or the hard way. Figure out isolated storage procedures and all the edge case exceptions.
There is also documentation and source code at that link so if you are interested in learning how to do it yourself you can start there.
If you implement the DLL it's going to be something like this.
void CameraTaskCapture_Completed(object sender, PhotoResult e){
//Doesn't have to be from camera capture. This is just the example from the documentation
//Just pass in a BitmapImage
EZ_Iso.IsolatedStorageAccess.SaveImage(“MyImage”, e.ChosenPhoto);
}
Then this is how you retrieve it
//This could also be a BitmapImage instead of an ImageControl.Source
ImageControl.Source = EZ_Iso.IsolatedStroageAccess.GetImage(“MyImage”,800,480);