<?php if(has_post_thumbnail() ) {
	$full_featured_img = wp_get_attachment_image_src( $post->ID, 'full-size');
	$portfolio_single_featured_img = wp_get_attachment_image_src( $post->ID, 'portfolio-single'); ?>
		<li class="slide">
			<a href="<?php echo $full_featured_img[0]; ?>" title="<?php the_title; ?>" rel="prettyPhoto[gallery]"><img src="<?php echo $portfolio_single_featured_img[0]; ?>" alt="<?php the_title; ?>" /></a>
		</li>
<?php } ?>