How to use png masks on canvas?

Question

JavaScript

There is a background image:
www.unoosa.org/res/timeline/index_html/space-2.jpg
and an alpha mask for the astronauts depicted against this background:
jim.studt.net/jpeg-alpha/astronaut-256-mask.png
How, use this mask to depict astronauts of different colors against this background to get something like:

Answer 1

https://github.com/codepo8/canvas-masking