Controlling which picture is used for FaceBook thumbnail

The following code inserted into the header.php passes off the thumbnail in the article.

 <?php
if (is_home()) {
	echo '<meta property="og:image" content="http://www.amarketplaceofideas.com/wp-content/uploads/2013/04/Wavy-Arm-Guy.jpg"/>';
}
elseif (function_exists("has_post_thumbnail") && has_post_thumbnail() && !is_home() ) { 
	post->ID), full ); ?>
</p>
<meta content="<?php echo $thumbnail[0]; ?>" property="og:image" />
<?php } ?>
<p>