When WordPress 2.9 was released, bringing with it an “official” way to handle thumbnails, I was a little bit annoyed. I had tons of posts where I had existing thumbnails that would have to be somehow updated, or else I would have to come up with some clever way to be backwards-compatible. So I just put it out of my mind and left things the way they were…until this year.

Redesigning gave me an excuse to modernize a lot of the stuff going on behind-the-scenes, and one of the things I improved was the handling of post thumbnails. The solution was easy: write a function to handle two methods of applying a thumbnail, and check both places for a thumbnail. The code looks something like this:

function my_smart_thumbnail($postid) {
$custom_field = get_post_meta($postid, 'thumbnail', true);
if ( has_post_thumbnail($postid) ) {
$featured_img = get_the_post_thumbnail($postid, 'thumbnail');
echo '<div><a href="'.get_permalink($postid).'">'.$featured_img.'</a></div>';
}
elseif ( $custom_field ) {
echo '<div><a href="'.get_permalink($postid).'"><img src="'.$custom_field.'" /></a></div>';
}
}

And then, in the Loop, where I want the image to appear:

<?php my_smart_thumbnail(get_the_ID()); ?>

With that, the old thumbnails keep working, but moving forward the new thumbnails take precedence.

Unfortunately, this new feature raises a new problem. What if you already have an existing, custom field-based, thumbnail solution? How can you easily (and optimally) move from one to the other?

I have another blog running a plugin called Wordbooker. It automatically syndicates links to my posts on Facebook. It can include the posts’ thumbnails when it does so, but it relies on WP 2.9’s way of doing things. Facebook “fans” won’t see the nice images by the links unless I were to migrate from custom fields to the new built-in thumbnail feature. How do I do that?

I could update my template to use PHP “if” statements to determine which method it should use for each post, and just use the new thumbnails for new post. That seems a little clunky though. Another, cleaner, option would be to have a look at the SQL columns and build a query to create the new thumbnails.

This seems like a great opportunity for a plugin developer. A single-use “importer” that reads an inputted custom field and iterates through all of your posts, creating the new thumbnail entries.

There are several services that can generate thumbnails like that, but most of them place watermarks on the images or place limits on how many API calls you can make in a month. (Amazon used to offer a paid service, but it was discontinued a year or two ago.)

To my surprise, when I was submitting an article to WPVote recently, I found that the thumbnails were served up by a subdomain of WordPress.com. I thought something along the lines of “Eh? I didn’t know they offered a screenshot service…” and continued about my business.

A couple days later, I spotted Ben’s blog post in my feed reader. In it he explained how he discovered a dynamic URL that Automattic uses, in places like the WordPress.org commercial themes page, to display thumbnails. He posted an email to Matt Mullenweg about it and got this as a response:

You can use it and link to it, but it’s not official. It’s not worth the effort to try to make it into a business – we have to support it anyway for our own apps.

Sounds good to me. Obviously it wouldn’t be nice to use it for something huge and high-traffic, but it seems like they don’t object to us smaller WordPress fanatics making use of it.

http://s.wordpress.com/mshots/v1/http%3A%2F%2Fprothemedesign.com%2F?w=250

There’s now a WordPress plugin that makes it easy to use the thumbnails in blog posts, with a shortcode, or elsewhere with a template tag.

Do you often put images in your posts? You probably upload them through the media manager built right in to the WordPress post editor. Every time you upload an image, it’s associated with the post you first attach it to. And WordPress creates a thumbnail to go along with it, of the size specified in the media settings.

Web Developer Plus has a an article on how to automatically find the thumbnail URL of the first image attached to a post and store it in the variable $img, which you can then echo out into an <img /> tag wherever you want the thumbnail to appear.

<?php
//Get images attached to the post
$args = array(
 'post_type' => 'attachment',
 'post_mime_type' => 'image',
 'numberposts' => -1,
 'order' => 'ASC',
 'post_status' => null,
 'post_parent' => $post->ID
);
$attachments = get_posts($args);
if ($attachments) {
 foreach ($attachments as $attachment) {
 $img = wp_get_attachment_thumb_url( $attachment->ID );
 break;
 }
}
?>
<img src="<?php echo $img; ?>" alt="Post Thumbnail" />

That’s a bit easier to handle, isn’t it? Once you have it set up, you don’t have to mess around with custom fields whenever you write a new post.

How To Use Thumbnails Generated By WordPress In Your Theme [Web Developer Plus]