Yes, apply style directive to the body tag. Copy the following style
between the head tags in the HTML view of the page. Change the url of
the image to correspond to yours. I don't think you can stretch it. If
you need bigger size, create a bigger version of the picture with an
image editing program.
<style>
BODY {
background: white url("images/pic1_small.jpg");
background-repeat: no-repeat;
background-position: center;
}
</style>
See this for explanation
http://www.w3.org/TR/REC-CSS2/colors.html
...PC