I am laying out an image gallery on a webpage and have several thumbnails of objects. How would I go about giving a visual clue that there is group of images behind each thumbnail? For example...lets say that I have a car as one of the thumbnails, that, when clicked, will show a large version of that car photo with nav arrows on the sides so the user can view more photos of that same object (slideshow).
Right now, the car thumbnail has a transparent magnifying glass on top of the thumbnail to show that it's clickable.
How should I give a visual clue on the thumbnail area to show that there's more photos "behind" that thumbnail and not just the larger version of that thumbnail? Or, is this extra affordance even necessary?
Note: I am using JQuery lightbox for the photo gallery.