The lightbox shows an image title for each image.
If not explicitly specified (via data-image-title attribute) the image title attribute is displayed and if empty the alt attribute.
The image (mouse-over) title often say something like "click to open lightbox" and that is no good title for the image in the lightbox. We therefore now first check the more meaningful alt attribute and use it as image title if not empty.
Specify a custom title via data-image-title attribute if you need a custom title other then the alt-attribute.