How to add any text to lightboxed image

I use the prettyphoto lightbox option. I’d like to find any way to add text to the larger photo that pops up when I click the thumbnail. The thumbnail displays the alt but the lightboxed photo doesn’t. Here is an example of my PHP code:

$photo_title = esc_html(get_user_meta($profile_user_id, “historical_photo_1_description”, $single ));
$historical_photo_1_url = ‘/wp-content/uploads/’.$historical_photo_1;
$historical_photo_1_tp = get_photo_thumbprint($historical_photo_1) ;
$historical_photo_1_tp_url = ‘/wp-content/uploads/’.$historical_photo_1_tp;
echo(‘‘);

On mouseover the thumbnail displays the intended text, but when the larger photo gets displayed, nothing displays either static or when mouseovered. Do I need to add a caption to the lightboxed larger image?