how to replace Post navigation to image

hi,

is it possible to print the image in the (‘%link’) in the poste nav, to show the next and previous thumb?

<div class=”post-nav”>
<span class=”previous”><?php previous_post_link(‘%link’) ?></span>
<span class=”next”><?php next_post_link(‘%link’) ?></span>
</div>

the thumbnail i want to show:
<img src=”<?php $values = get_post_custom_values(“thumb”); echo $values[0]; ?>” title=”<?php the_title(); ?>”/>

Thanks