I want this blog to have a full screen image as background, if you using wordpress feature to set background feature you can’t do it. If you the easy way to make a full image for background you can search with google for that.
I found the easy solution for this purpose, I found it on wordpress forum and from http://css-tricks.com/perfect-full-page-background-image/
Add this code on your style.css
background: url(../images/texture.png) no-repeat center center fixed;
save it and refresh to you website