This is pretty easy.
//Include this above your loop
$i = 0; //Counter
if(have_posts())while(have_posts())the_post();
//include this in your loop
$i++;
if($i <= 5)
echo "<img src="http://urltoinewimage" alt="Image Title" />";
//Stop including in your loop
the_title();
the_content();
endwhile; else:
endif;