Author Avatar as default first image

There was a lotta junk in that function, here’s all you need:

function get_post_image() {
    global $post;

    if ( preg_match( '/<img.+?src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches ) )
        $image = $matches[1];
    else
        $image = get_avatar( $post->post_author );

    return $image;
}