gistfile1.php

<?php

//shortcodes inside posts
function diww_include_post($atts) {
  $thepostid = intval($atts[id]);
  $output = '';
  $post = get_post($thepostid);
  if ($post) :
    $output .= '<a href="' . the_permalink() . '">' . get_the_post_thumbnail($post->ID, 'large') . '</a>';
  else :
  // failed, output nothing
  endif;

  return $output;
}

add_shortcode('include_post', 'diww_include_post');