Yes, This is my tut. I know some other people may have said it but i found this way on ym own. No Hating/Flaming Please
Note, This Does Not Require ANY Modding experience, NOR do you need your profile on your flash drive!

1. Put Your Flash Drive Into Your Computer

2. Choose A Picture You Want As your New Theme

3. Create A New Folder Withing the flashdrive, you can name the folder whatever

4. Drage the photo Into the new folder

5. Put the flash drive into your xbox

6. Go to photo library (I Believe Its Under The My Xbox Category, Could Be wrong)

7. If it asks what storage device Choose The Flash Drive

8. Choose The Folder you saved it in

9. And hit Y On the picture, it should say something like picture options, and then choose set as background, wallpaper, or theme i forget!

Now enjoy.

Please Note that some of the picture may be cut off due to the NXE dashboard