How to show featured image when mouse hover a link?

Hello guys,

Maybe someone can help me...

Lets say that I have a link in my site:

<a href="url">text</a>

Code (markup):

How can I show the post featured image when I put the mouse hover the link?
Does anyone know any good method or plugin to do that?

Thank you guys!

 

I have found this method and is almost done:
http://www.dynamicdrive.com/style/csslibrary/item/css-popup-image-viewer/

The only issue that I have now is to show a custom post type feature image in my single.php.

I am trying this code:

<?php the_post_thumbnail('freeGallery', array('class' => 'imgthumb')); ?>

PHP:

But without success...
It shows the post (single.php) featured image and not the custom post (freeGallery) featured image.

What Im doing wrong?
Can please someone help me?

Thanks!!

 

This is my code, but isn't working... Is only showing the post featured image and not the custom post type featured image.
Can someone tell me what I'm doing wrong?

<?php
$loop = new WP_Query(array('post_type' => 'freeGallery', 'post_status' => 'publish'));
?>
<td><div class="gallerycontainer">
<a class="bestthumbnail" target="_blank" title="<?php echo $post_title; ?>" href="<?php echo get_post_meta($ID,'mr_freeGalleryUrl',true); ?>" rel="nofollow"><?php $title = $post_title; if (strlen($title) > 85){ echo substr($title,0,85).'...';}else { echo $title;}?><span><?php the_post_thumbnail('freeGallery', array('class' => 'imgthumb')); ?></span></a></div></td>

PHP:

Thanks