Obviously, one can do this as-is in a text/html module. Add Mandeep's Live Images module to provide an automatic means of adding the lightbox overlay when the image thumb is simply linked to the larger image file.
You could also create this in either Mandeep's Live Content, Ventrian's Property Agent, or possibly WildModule's Portfolio. A successful implementation with any of these will require a fair amount of thought and effort, but they all would result in a manageable product for the client. Somewhat easier would be doing it in Ventrian's Simple Gallery. but you'd have to revise the layout a fair bit. Note however that Simple gallery is the only module that creates good quality resizes.
If you're happy coding, then you can also do it in some of the forms modules, but that's a different learning curve and may not provide a workable content management experience for the client.
Given that the client is a human being with a brain, and is keen to do it themselves, I would spend the time on a little training. All that is needed for adding a new artwork is a couple of resized images and basic working knowledge of the core Text/HMTL module. Most people could manage that with a couple of hours of training and a tip sheet.
Rob