If you have recently downloaded the latest WordPress 2.9 beta build (like I have) you will find “the_post_image” no longer works! In place you will see that lovely “Fatal Error” message above.

“Post/Page Image was too generic a name. Post/Page Thumbnail is more clear, even if you can create very large thumbnail images if you so choose.”

- WordPress trac

Below, I will be noting the changes found in the latest build, and how to now use thumbnails in a WordPress theme using 2.9′s post thumbnail function.

Adding support for the post thumbnail feature in a theme

This part has not changed. Just add the code below to your themes function.php

if ( function_exists( 'add_theme_support' ) )
	add_theme_support( 'post-thumbnails' );

So, what has changed?

the_post_image to the_post_thumbnail

old:

<?php the_post_image( 'thumbnail' ); ?>

New:

<?php the_post_thumbnail( 'thumbnail' ); ?>

<?php the_post_thumbnail( 'medium' ); ?>

<?php the_post_thumbnail( 'full' ); ?>

Checking if a post has an image

Old:

<?php
	if ( has_post_image() )
		the_post_image( 'thumbnail' );
	else
		echo '<img src="default-thumbnail.jpg" alt="Default Thumbnail" title="Default Thumbnail" />';
?>

New:

<?php
	if ( has_post_thumbnail() )
		the_post_thumbnail( 'thumbnail' );
	else
		echo '<img src="default-thumbnail.jpg" alt="Default Thumbnail" title="Default Thumbnail" />';
?>

Getting the post image ID

Old:

$image_id = get_post_image_id();

New:

$image_id = get_post_thumbnail_id();

This is a developing post…