Wordpress Themes - WP Forum at BFA - bg image for blog page (post container)

I am using ATA 353
There is a static front page and a blog page named "Blog."
I am trying to place a background image only on the Blog page, not in the posts.

I used this code in the "above the loop" and "the loop" sections:

Code:

<?php if ( is_home() ) { 

echo '<img src = "/wp-content/themes/atahualpa353/images/blog_center-background.gif" />';} ?>

The problem is... the image is pushing the posts down below it.

Could someone explain what code I should use to make this a bg image so it sits behind the post excerpts?

Thanks in advance.