There're 2 things you need solve in this interaction:
- How can I tell users that there're related images?
- How should I show the full collection?
Depending on your development resources, there're 2 ways to approach the first problem. The easy way is to simply put a text link under the image that would read
See X related, like this:
download bmml source – Wireframes created with Balsamiq Mockups
The hard way is to create a semblance of a stack of images and put a badge in the lower right corner (conventionally) to indicate the number of related images. It's not necessary to use the actual related images in the stack (saves processing & rendering times) as long as it's clear which image has related items and which doesn't. It would look something like this:
download bmml source
The second problem is much easier to solve. You can expand the collection of images into either a dedicated page or into a modal sub-window (or a dialog - depends on your users' workflow).
Since the OP has added a mockup of the interface, I can definitely say that stacks and modals will work best in his situation. For everyone else, the aforementioned choices are still valid.