template tag in a php echo – how???

I’m trying to get this working… but all in comes up with is the url…
http://xyz.com.au/wordpress/wp-content/uploads/venue.jpg

I want…
http://xyz.com.au/wordpress/wp-content/uploads/venue64.jpg where 64 is the post ID

<?php if ( in_category(17) || in_category (5) ) {
echo '<a href="http://xyz.com.au/wordpress/wp-content/uploads/venue'.the_ID().'.jpg"><img class="alignright size-medium" src="http://xyz.com.au/wordpress/wp-content/uploads/venue'.the_ID().'.jpg" width="300px" title="'.the_ID().'" ></a>';
} else {
echo '<p>nothing here</p>';
}
?>