If you just need the location of the image it is provided in the OriginalFileName property of the PhotoResult that you get from the Completed event.
For example, take a picture with the emulator gives "C:\Data\Users\Public\Pictures\Camera Roll\WP_20140106_002.jpg"
Now that you have it you can display to the user with a BitMapImage and set that as the Source for an image.
MyImage.Source = new BitmapImage(new Uri("C:\\Data\\Users\\Public\\Pictures\\Camera Roll\\WP_20140106_002.jpg", UriKind.Absolute));
If you need the image right away, you get that from the ChosenPhoto property of the PhotoResult.