Prompt in words, but expect the value in numbers, eg: "Twenty-five" and the box requires you to type "25"? At least this specific case, it would require you to type it.

yeah, that would possibly stop the copy and paste problem. to make it robust they would need to use a string of a few non-visible characters but that would fail if the browser's clipboard system doesn't copy them over for some kind of privacy initiative. might be another way it fails that I can't think of right now.