Another clever thing found at W3schools. The magnifying glass runs from a bit of Java script found in a html element with the class name .magnifier-related. If you open the script, right at the bottom of it you will see this line:
magnify("#myimage img", 3);
The number is showing how strong the magnification will be, in this case 3 times. It can be edited. The limits will of course depend on the size and quality of your image.
When a page with this component is opened, you might initially see just a circle instead of the actual magnifying glass. The magnification is not to start before the image is fully loaded, so you may have to refresh the page, especially by slow connections.