In Robo Gallery you can use few different ways to accomplish this task.
For example: for configuration of the hover effect for the thumbnails you can use pre-configured options for title or description of the gallery image and enable or disable this elements randomly, depend of your needs.
Another, more advanced, option for configuration of the hover overlay layout it’s template option which you could enable in gallery settings / hover settings section.
If you switch to template mode for the hover basic settings for the configuration of the title and description text will be turned off and you get access to the field where you can modify template for this gallery interface element.
In template field you can modify layout using HTML/CSS elements and some build-in tags. You can use mix HTML divs or tables with tags like: title, description, link and zoom button tag and etc. So here you can full freedom with customization of the gallery hover layout. You can even add some custom CSS buttons for the gallery picture overlay effect.
If we talk about image description text in Polaroid gallery mode you can use there one from three text elements which you have for every gallery image. Namely: image title, image description and image caption.
In Polaroid settings and in gallery lightbox settings you free to select which text elements of the images you gonna have as source for the content on both of this locations and actually you don’t have to use the same test for the image description panel in Polaroid gallery mode and in gallery lightbox description panel.
For example: in polaroid mode you can use title of the images but in lightbox description of pictures caption text.
Please try and let me know if you’ll have some other questions.