I found and modified a chunk of code found here: http://www.wprecipes.com/wordpress-tip-detect-if-a-post-has-at-least-one-image.

    <?php 
    while ( have_posts() ) : the_post();
        $content = $post->post_content;
        $searchimages = '~<img [^>]* />~';
        preg_match_all( $searchimages, $content, $pics );
        $iNumberOfPics = count($pics[0]);
        if ( $iNumberOfPics > 0 ) {
            //your loop content goes here
        } 
    endwhile; 
    ?>

I think this just looks for images entered in the rich text editor - if you want to check for featured images as well you'll likely have to add something.  Check out [`has_post_thumbnail`][1].


  [1]: http://codex.wordpress.org/Function_Reference/has_post_thumbnail