What is contained in the emperor.png file? It depends on how you look at it. First open it in your favorite image viewer or editor. (Second favorite is OK too.) Then, browse to the emperor.html file and view it by following directions there.
Note that the html and png files must be accessed via a web server. Accessing them directly via your local file system will not work due to browser security constraints. You should be able to access via the github server here: https://isaacpacht.github.io/TheEmperorsNewImage/emperor.html
If that's too much work, you can watch the demo instead, although it doesn't play very smoothly for some reason (and anyway, it's much more fun to click the button yourself).
Tested on Chrome 77