For my xbox 360, how can i set my theme{back round picture} that i downloaded into my 360 as a gamer picture?

I downloaded it myself from a portable device. It didnt come with it.For my xbox 360, how can i set my theme{back round picture} that i downloaded into my 360 as a gamer picture?No. You have to use a theme format. Not a gamer picFor my xbox 360, how can i set my theme{back round picture} that i downloaded into my 360 as a gamer picture?you cant

u have to download a theme instead