It doesn't seem like canvas defender replaces HTMLCanvasElement.prototype.getImageData anyway, so one could simply use that to generate a hash. Hiding the fact

It doesn't seem like canvas defender replaces HTMLCanvasElement.prototype.getImageData anyway, so one could simply use that to generate a hash. Hiding the fact that the function in non-native requires replacing Function.prototype.toString with something that will return a fake result if the function being tested is one of the modified ones. If an userscript replaces that toString prototype before you can grab it, I'm unaware of any other way to test if a function is native.