It’s very simple with WordPress 2.9+, all you need is a few lines of code in your functions.php.  So, therefore we need to open functions.php as well as index.php.

The Function

In your functions.php place this code and tweak as necessary:

<php
add_theme_support( 'post-thumbnails', array( 'post' ) );  //displays thumbnail for only posts
set_post_thumbnail_size( 50, 50, true );  //50 pixels wide by 50 pixels long, box resize mode
>

Placing the Thumbnail

Wherever you would like the thumbnail to appear place this code:

<php
if ( has_post_thumbnail() )  echo the_post_thumbnail();
else {
echo '<img src="http://yourdomain.com/default.png" />';
}
>

This tells WordPress that if this post has a thumbnail uploaded (we will get to that in a moment), display it; otherwise display the default image.

Uploading the Thumbnail

How do you upload a thumbnail?  When adding a new post, under categories look for “Post Thumbnail” and click “Set thumbnail”.

Of course, this can be styled and tweaked to your needs so have fun tweaking and thanks for reading!

Image by by David Reeves