Image Popup Example
Click image to popup the larger image with the alt text as the caption. Adapted from this example at W3 Schools.
Popups are often called a "Modal." To see the code and instructions on the steps you need to take to get this to work, right-click and view page source. Be careful not to click on the image as that will trigger the popup. Right click anywhere above the image. This will only work on a single image. To do a gallery, you should find a more robust javascript source such as Magnific Popup.