Trying to change image funtion from enlarge image to redirect to amazon website

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The call to rel="prettyPhoto" is what makes the lightbox popup the image. If you remove that the lightbox will no longer popup.

Now as far as redirecting the user straight to the product page on Amazon, you need to change;

href="https://wordpress.stackexchange.com/questions/104566/<?php get_image_url(); ?>"

to…

href="https://wordpress.stackexchange.com/questions/104566/your_link_to_amazon_product_page_jere"

I don’t know where you are storing that link, if at all? Are you storing the link to the product in a custom field? If so, you could do something like;

<div class="pro-snap">
<?php
if ( has_post_thumbnail() ) { ?>
    <a href="https://wordpress.stackexchange.com/questions/104566/<?php echo get_post_meta($post->ID,"meta_key', true); ?>"  title="<?php the_title(); ?>" ><img class="boximg" src="<?php bloginfo('stylesheet_directory'); ?>/timthumb.php?src=<?php get_image_url(); ?>&amp;w=200&amp;zc=1" alt=""/></a>
<?php } else { ?>
    <img class="boximg" src="<?php bloginfo('template_directory'); ?>/images/dummy.png" alt="" />
<?php } ?>
</div>

Where meta_key in the example below is the name of the custom field in which you have stored your product link;

<?php echo get_post_meta($post->ID, 'meta_key', true); ?>