Things Needed:
1. Computer
2. Xbox 360
3. USB Drive (Memory Stick) or SD Card Reader
Note: You don't always have to use a usb drive. If you have an SD Card and a memory card reader, you can use that too.
Steps:
1. Open a program such as Paint, CorelDraw, or GIMP.
2. Create Your Own Picture
3. Insert Your USB Drive or SD Card Reader into your computer.
4. Save the picture you made. (Save it as a JPG or JPEG. Not as any other image file.)
5. Copy the picture on to your USB Drive or SD Card Reader.
6. Insert the USB Drive or SD Card Reader into the Xbox 360.
7. Go to Photo Library and select "Portable Device".
8. Find the Picture You Made.
9. Click the Y button(It might be the X button If it does not work.)to Set the Picture as Your Background.
10. Done. Back out of Photo Library and look at your picture. Enjoy!