You have surely seen my little earlier article here
which is about to convert a very nasty gray-scale image into a much nicer gray-scale image.
This is what the free FotoSketcher software does:
I prefer to print out the improved gray-scale figure and to do all the following editing with a pen and liquid paper.
But there is also an easy way to do this digitally, on your computer. The picture on the top of this page shows the result that you can reasonably expect.
I am using the much under-estimated Windows PAINT app. The Windows PAINT app comes free, together with the Windows operating system.
Here is a video that shows you how I am using PAINT to do this.
I only do this myself when I cannot avoid it. Better let your assistant convert raw gray-scale images into clean line drawings if you are a lawyer.