The current CAPTCHA system fails every one of those requirements, I'd
suggest either using a more common captcha type (such as Google
reCAPTCHA, hCaptcha or a generic maths challenge), switching to more
human friendly, easily Googleable, but still domain specific questions
On the one hand, you say to make it more difficult, on the other hand, you say to make it easier.
Obviously, this captcha is just to weed out the barest minimum of script kiddies.
Like, changing your SSH port isn't the same as securing your system, but it gets rid of 99% of the automated attacks.
This current captcha also works great for people with visual impairments as the commands they need to run are all text based.
FWIW: I'm not in charge of any decisions here, just giving my opinion
