Tracing paper is common tool for illustrators and graphic designers.
I wrote a tool which is able to convert clicks on image into coordinates and use it in JavaScript.
Launch Tracing Paper JS in full screen mode
Just click at the image and tool will record set of coordinates as JavaScript code.
It’s simple app written in JavaScript with AngularJS.
Source code is available at Github: https://github.com/georgik/tracing-paper-js