Get Last Posts with Thumbnail Shortcode

It can be edited a little bit, to have the option to get the featured image and if empty, then to get the thumbnail. You can pick what you like.

function catch_that_image() {
global $post, $posts;
$first_img = '';
ob_start();
ob_end_clean();
$output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
$first_img = $matches [1] [0];

// no image found display default image instead
if(empty($first_img)){
$first_img = "/images/default.jpg";
}
return $first_img;
}

function my_recent_posts_shortcode($atts){
 $q = new WP_Query(
   array( 'orderby' => 'date', 'posts_per_page' => '20', 'category' => 'web-design,graphic-design' )
 );

$list = '<ul class="recent-posts">';

while($q->have_posts()) : $q->the_post();

 $list .= '<li><img src="'.catch_that_image().'" width="50" height="50"' . '<a href="' . get_permalink() . '">' . get_the_title() . '</a>' . '<br />' . get_the_excerpt() . '</li>';

endwhile;

wp_reset_query();

return $list . '</ul>';

}

add_shortcode('recent-posts', 'my_recent_posts_shortcode');