Show only Post titles with thumbnails in category pages

In my category page full post are showing up. I want to make it only post titles with tumbnails. I'm using wordpress Twenty twelve theme.

 

Paste the code you are using now. You are going to want to remove the_content and add something like this where you want the thumbnail to go

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

PHP:

 

oops forgot to mention. for <?php postimage('thumbnail');?> to work, add this to header.php

<?php
function postimage($size=thumbnail) {
if ( $images = get_children(array(
'post_parent' => get_the_ID(),
'post_type' => 'attachment',
'numberposts' => 1,
        'order' => 'ASC',
        'orderby' => 'ID',
'post_mime_type' => 'image',)))
{
foreach( $images as $image ) {
$attachmenturl=wp_get_attachment_url($image->ID);
$attachmentimage=wp_get_attachment_image( $image->ID, array(300,500));
 
echo $attachmentimage;
}
} else {
echo "No Image";
}
}
?>

PHP:

 

I used CSS to hide contents in category pages. Here is what I added.
.category .entry-content, .category .entry-summary, .archive .entry-content, .archive .entry-summary { display: none; }
My blog link http://www.digitaladvices.com/

 

There should be a plugin for that if I'm not mistaken.