Jquery Masonry feature image margin/padding issue

I’m currently working on a theme with the Jquery Masonry plugin integrated. This plugin makes it possible to float your elements in a nice way, instead of keeping big gaps while floating.

Masonry is a layout plugin for jQuery. Think of it as the flip side of CSS floats. Whereas floating arranges elements horizontally then vertically, Masonry arranges elements vertically then horizontally according to a grid. The result minimizes vertical gaps between elements of varying height, just like a mason fitting stones in a wall.

All the featured images of the page should be stacked seamlessly without gaps between the elements. ‘Seamlessly’ is the idea, but each picture keeps approx. 3 pixels of white space below the picture. I cannot succeed to remove this. See an example of the website here.

When replacing the <?php the_post_thumbnail('full', array('class' => 'thumb')); ?> with <div style="width:420px; height:233px; background-color:#FC0;"></div> it works perfectly. No whitespace and everything is stacked seamlessly. The issue is probably the <img> inside the <div class="box">. I’ve tried to style the <img> in various different ways without success. Any suggestion is welcome.

index.php

<div id="wrapper">
	<?php if (have_posts()) : while (have_posts()) : the_post(); ?>

		<div class="box">
        	<a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>" >
            	<!-- TEST DIV.
                <div style="width:420px; height:233px; background-color:#FC0;"></div>
            	-->
			<?php the_post_thumbnail('full', array('class' => 'thumb')); ?>

                <span class="thumb-slide">
                    <ul>
                        <li><?php the_title(); ?></li>
                        <li><?php the_subtitle() ?></li>
                    </ul>
                </span>
             </a>
		</div>

	<?php endwhile; ?>

	<?php else : ?>

		<h2>Not Found</h2>

	<?php endif; ?>
</div>

CSS

#wrapper {
	padding: 0;
	margin-top: 20px;
	margin-right: 20px;
	margin-bottom: 80px;
	margin-left: 20px;
	}

.box {
  float: left;
  margin: 0px;
  padding: 0px;
	}

.box img {
	margin: 0px;
	padding: 0px;
	overflow: hidden;
	}

.thumb {
	margin: 0px;
	padding: 0px;
	}