But if your site already has hundreds of posts, adding a thumbnail image for each one will be a lot of work even if you only want the same image for each old post.

This plugin allows you to specify a default post thumbnail for posts that doesn’t have a thumbnail set.

This plugin requires that you have enabled support for post thumbnails in your theme (you can enable it by adding these 2 lines in your theme functions.php file).

if ( function_exists(‘add_theme_support’) ) {
add_theme_support(‘post-thumbnails’); }

You can select the thumbnail from the images already uploaded to your media library.

You can see more screenshots of this plugin, how to use it and the download link in the Default Post Thumbnails page

Now that WordPress 2.9 was released we can use new functions to display the post image as a thumbnail. This feature is only available if it is enabled specifically in the theme, so to enable it all you have to do is add this 2 lines to the functions.php file of your theme.

if ( function_exists(‘add_theme_support’) )
add_theme_support(‘post-thumbnails’);

This will enable the post thumbnail functionality and add a new box in your new post pages to set the post thumbnail

To set an image as thumbnail you upload it like any other image or select it from your media library and at the bottom you will see the text “Use as thumbnail”, click on it and that’s it.

Now, to display the thumbnail in your theme you have to use the function the_post_thumbnail(),  the basic usage should be :


if ( current_theme_supports( 'post-thumbnails' ) )
the_post_thumbnail(array(100,100));


Which is pretty simple, and integrated  into the code we have from the previous post about thumbnails should look like this:


if ( function_exists('has_post_thumbnail') && has_post_thumbnail() ) {
the_post_thumbnail(array(100,100));
} else {
postimage(100,75,'image for: '.get_the_title(),'image');
}


You can add this function to your theme functions.php to display the thumbnail image of your post or a default image if the post does not have one.

function postimage($width,$height, $text, $class) {
$scriptpath = get_stylesheet_directory_uri();
$attachments = get_children(array(‘post_parent’ => get_the_ID(), ‘post_type’ => ‘attachment’, ‘post_mime_type’ => ‘image’, ‘orderby’ => ‘menu_order’));
if (!is_array($attachments)) {
$image = $scriptpath.”/images/default.jpg”;
echo ‘<img class=”‘.$class.’” title=”‘.$text.’” src=”‘.$scriptpath.’/scripts/timthumb.php?w=’.$width.’&h=’.$height.’&zc=1&q=100&src=’.$image.’” alt=”‘.$text.’” width=”‘.$width.’” height=”‘.$height.’” class=”‘.$class.’” />’;
} else {
$img = array_shift($attachments);
$imagelink = wp_get_attachment_image_src($img->ID,’full’);
$image = $imagelink[0];
echo ‘<img class=”‘.$class.’” title=”‘.$text.’” src=”‘.$scriptpath.’/scripts/timthumb.php?w=’.$width.’&h=’.$height.’&zc=1&q=100&src=’.$image.’” alt=”‘.$text.’” width=”‘.$width.’” height=”‘.$height.’” class=”‘.$class.’” />’;
}
}

How to use it:
In your template add the function before the call to the_excerpt.

<? postimage(100,75,”image for: “.get_the_title(),’image’)?>
<? the_excerpt(); ?>

The parameters are:
$width & $height – the purpose of these is obvious
“image for: “.get_the_title() – This will become the title and alt text of the image in the tag
image – this is the class for the tag, with this you can align/float the image to the left/right or apply any style you already defined for the images

This function uses the timthumb script to resize and crop the image automatically. after downloading the script, create a subdirectoy named ‘scripts’ in your theme directory and copy the timthumb.php file to it. Now create a ‘cache’ subdirectory in your theme directory and assign it write permissions, so the script can create the images in that directory and skip the creation of the image on every page request.

If your post does not have an image, the function will display a default image. to define the default image upload the image you want to be used by default to your theme in the images directory and name it ‘default.jpg’