Create the map with a image background

Here is something you can do with Mathematica 7.0 Image Processing

Here is a good picture of  American Flag

Then create a mask for it and add them together:

mask= Graphics[{Black, CountryData["UnitedStates", {"Polygon", "Mercator"}]}, ImageSize -> {500, 335}]

flagImage = ImageAdd[img, mask]

 

Then create another new image with the boundary:

bgk = Graphics[{FaceForm[], EdgeForm[{Black}], CountryData["UnitedStates", {"Polygon", "Mercator"}]}, ImageSize -> {500, 335}]

ImageMultiply[bgk, flagImage]