title: how to get post thumbnail using post id in wordpress?
body: <p>I am trying to get the post thumbnail using post_id,but i am getting so many problems.</p>
  
  <p>Iam calling the function in a separate php file in theme directory</p>
  
  <pre><code>echo get_the_post_thumbnail('637');
  </code></pre>
  
  <blockquote>
    <p>Fatal error: Call to undefined function get_the_post_thumbnail() in ...</p>
  </blockquote>
  
  <p>1)can we get the thumbnail using post_id</p>
  
  <p>or</p>
  
  <p>2)can we get the image source using post_id</p>
  
  <p>please any body help me</p>
  
  <p>Thanks in advance</p>