How to keep spam off wordpress image attachments by not allowing comments on them.

Place the following in your theme’s functions.php file.

add_filter( 'comments_open', 'no_media_comments', 10, 2 );

function no_media_comments( $open, $post_id ) {

	$post = get_post( $post_id );
        // wordpress refers to images as attachments
	if ( 'attachment' == $post->post_type )
		$open = false;

	return $open;
}