WP8

Handling multi-resolution in WP8

How they shoulda done it

aka: How it works in Windows 8

wvga

800 x 480 (15 : 9)

wxga

1280 x 768 (15 : 9)

720p

1280 x 720 (16 : 9)

msdn documentation

var imagePath = string.Format(
    "/Resources/Images/Scaled/720P/{0}", imageName);

scaledImageUri = new Uri(imagePath, UriKind.Relative);