Make a lightbox script use both the image caption and description as the title for when the image is enlarged.

gistfile1.php

<?php
/**
 * Filter Easy Image Gallery HTML to add description
 *
*/

function my_child_theme_easy_image_gallery_description( $html, $rel, $image_link, $image_class, $image_caption, $image, $attachment_id, $post_id ) {
	
	// get the image's description	
	$image_description = get_post( $attachment_id )->post_content ? get_post( $attachment_id )->post_content : '';

	// add the description to the title attribute
	if ( function_exists( 'easy_image_gallery_has_linked_images' ) && easy_image_gallery_has_linked_images() )
		$html = sprintf( '<li><a %s href="%s" class="%s" title="%s - %s"><i class="icon-view"></i><span class="overlay"></span>%s</a></li>', $rel, $image_link, $image_class, $image_caption, $image_description, $image );
	else
		$html = sprintf( '<li>%s</li>', $image );

	return $html;
}
add_filter( 'easy_image_gallery_html', 'my_child_theme_easy_image_gallery_description', 10, 8 );