Conditionally Displaying Custom Fields with WordPress

display_custom_fields.php

/****************************************************************
*                                                               *
*  Conditional statement to retrieve content based on the       *
*  existence of a Custom Field.                                 *
*  If the Custom Field exists, display the content of the       *
*  Custom Field (can be adjusted to display alternate content). *
*                                                               *
****************************************************************/

// Check for existence of content in that custom field
<?php if (get_post_meta($post->ID, 'image_url', true)): ?>

  // if there is content, do something with it - in this case, display an image
  <img src="<?php echo get_post_meta($post->ID, 'image_url', true) ?>" alt="Your alternate text" />

  // if there is no content
<?php else: ?>
  
  // display some alternate content, in this case, a placeholder image
  <img src="http://placehold.it/215x215" />

<?php endif; ?>