calling caption associated with a specific image

I am using the magazeen Theme which is inserting timthumb resized images into posts by pulling them directly out ouf the upload directory. In order to facilitate this the user needs to enter the Images code as a custom field.

Now, I was wondering if it was somehow possible to retrieve the information wordpress has associated with this image, the caption in particular.

Below is the code used to pull the image, I imagine the to pull the caption I would have to use a similar code.

<a href="<?php bloginfo( 'template_directory' ); ?>/timthumb.php?src=<?php echo get_post_meta( $post->ID, "image_value", true ); ?>&w=600&h=600&zc=1" rel="lightbox" title="<?php the_title_attribute(); ?>"><img src="<?php bloginfo( 'template_directory' ); ?>/timthumb.php?src=<?php echo get_post_meta( $post->ID, "image_value", true ); ?>&w=225&h=246&zc=1" alt="<?php the_title(); ?>" /></a>