Different backgrounds

Hello there, I’m trying to get different backgrounds on each page. I have the following code:

<?php if (have_posts()) : ?>

		<?php while (have_posts()) : the_post(); ?>

			<div class="post" id="post-<?php the_ID(); ?>">

				<div class="entry">

                                        <?php
		if( is_page(40) ) {
                        $img = 'http://www.bigtukker.nl/images/content-geschiedenis.gif';
		} if( is_page(82)){
			$img = 'http://www.bigtukker.nl/images/content-toekomst.gif';
                } if( is_page(49)){
			$img = 'http://www.bigtukker.nl/images/content-gallerij.gif';
		} if( is_page(55)){
			$img = 'http://www.bigtukker.nl/images/content-nieuws.gif';
		} if( is_page(57)){
			$img = 'http://www.bigtukker.nl/images/content-links.gif';
		} if( is_page(35)){
			$img = 'http://www.bigtukker.nl/images/content-home.gif';
		}
                ?>
                <img src="<?php echo $img; ?>" />
                <?php the_content('Read the rest of this entry &raquo;'); ?>

				</div>

The problem is that the background is above the content. Can anyone help me?