Creating a pdf file from Storyline running under an LMS

Happy to help. 

Having re-read you question - I guess I should also point out that my original error was not my code - but that I was trying to run the code above from a compiled version of my Storyline course on my local PC.

That won't work because the browser is complying with with the CORS (Cross Origin Resource Sharing) security protocol designed to prevent malicious files being loaded. Ironically, files on the same PC accessed via a file reference i.e. no "http: address" are not assumed to come from the same "origin" and therefore trigger a CORS error when the HTTP request to load the image (addImage) is executed.

When I moved the code and ran it on a server (I have my own cloud server but you could use Amazon or Microsoft Azure Cloud storage) the code runs fine because the file is accessed via it's http: address and the img.CrossOrigin ="": command basically tells the browser to accept an 'anonymous' unauthenticated image i.e. switch off the CORS check in the HTTP request.

Sorry that got a bit technical. In simple terms, you have to load the compiled web code with the image in the root folder onto a server for it to work - it won't work if you run it on your PC.