You won't be able to accomplish this within an email itself. If you wanted to do this on a landing page, there's code that you can use to create a magnifying glass effect, or open the image in a modal window.
Generally the easiest thing to do, and would work fine for your scenario also, is just link to a larger version of the same image in a new tab. So save two versions of the image, one that's small and compact for the email, and one that's full size. Link the email one to the full one.