Get Image Description

function wp_get_attachment( $attachment_id ) {

$attachment = get_post( $attachment_id );
return array(
    'alt' => get_post_meta( $attachment->ID, '_wp_attachment_image_alt', true ),
    'caption' => $attachment->post_excerpt,
    'description' => $attachment->post_content,
    'href' => get_permalink( $attachment->ID ),
    'src' => $attachment->guid,
    'title' => $attachment->post_title
);
}

Source

As sporkme explains later in the thread, this is dumped into your functions.php and can then be called with $attachment_meta = wp_get_attachment(your_attachment_id);.