If the picture is visible on the web, right click on the picture and select properties. That will provide you the URL of the photo.

You can upload you picture to Tinypic.com copy the URL of your piicture then paste that URL into your channel design picture box

if you right click on the picture and then click on properties, it should show the url.

The little picture to the left of the URL in the address bar is called a favicon.

You can easily adjust the background of a web page as a picture. It can be set as : background-image="url('url-source')."