This snippet by Balázs Suhajda lets you mimic the effect of a magnifying glass. With this snippet, your image is converted to greyscale on hover we see a magnifying glass effect by zooming into the image and this section is shown with colour. You can move around and this section with your mouse.
If you are having trouble with the pen, try the archived copy on GitHub
Magnifying Glass Effect Snippet
See the Pen Image zoom by Balázs Suhajda (@suhajdab) on CodePen.0