Undefined Variable (Displaying image via custom field)

Question

I'm getting "an undefined variable in line 6" while trying to display an image from a custom field. It's pulling the name/link of file; but not image. Here is my code

<?php query_posts( 'cat=36&post_type=athletes&showposts=1&orderby=rand'); ?>
     <?php if (have_posts()) : while (have_posts()) : the_post(); ?>
  <article id="post-<?php the_ID(); ?>" <?php post_class('clearfix'); ?> role="article" itemscope itemtype="http://schema.org/BlogPosting">
  <a href="<?php the_permalink() ?>">Read More</a>

 <?php $imageid = get_post_meta($post->ID, 'athletethumbnail', true); ?>
 <img src="<?php echo wp_get_attachment_url( $imageid ); ?>" height="192" width="192" />
          <?php the_title(); ?>

  </article>

  <?php endwhile; ?>
  <?php else : ?>
  <?php endif; ?>

Answer 1

Try this:

<?php $imageid = get_post_meta(get_the_ID(), 'athletethumbnail', true); ?>

Also, you might want to read this.