How to draw on a canvas with an image?

Question

JavaScript

There is a code: https://jsfiddle.net/3ab9vc0L/
When you click on the 256x256 button, an image is drawn on the canvas Tell me
how to make it possible to draw with a pencil (drawing occurs when you click the mouse) over the image?
Example:

How the pencil works - when you click on the canvas with the mouse, the photo now disappears and the default background appears and a pixel with a new color is already drawn there (the color is visible in the Current Color button)