change full image link

please help me 🙂

ok im running 3.5.1 a gallery template. ok you click the thumb go to the attachment page a big picture that is link to the full path of the pic ex.

/wp-content/uploads/2011/11/219.jpg

is there a way to add a affiliate link instead of the full pic?

<div class="attachment-image"><a href="<?php echo wp_get_attachment_url(); ?>"><img src="<?php echo wp_get_attachment_url(); ?>" alt="<?php the_title_attribute(); ?>" /></a></div>

im guessing i swill have to make a table in the adding galley part so i can add one url and it will be added to all the big thumbs for the gallery.