This video shows you how to give your YouTube account a background image. Basically what you do is take any image that you would like to have as your background and upload it to a image uploader of your choice. Once the image is hosted it should show a url link to the file, copy this link. Then under your YouTube account settings scroll down to channel design. From here you should see a box that asks for a background image url, paste the url into this box click yes for background image and update your changes.