I know some quite clever people who could not solve this, for different reasons. One of the brightest, quickest witted people I know experiences significant dy

I know some quite clever people who could not solve this, for different reasons. One of the brightest, quickest witted people I know experiences significant dyslexia and dyscalculia. She would fail at this and it would make her quietly angry at you for making her go through it. I also know someone with a vision disorder who would struggle. Hell, when I am tired, I would have to close one eye to pass -- I have this issue with quite a lot of captchas, and I am not legally vision-impaired. And I would be angry at the developer for making me struggle. Furthermore, I think in a world with an ageing population it might be worth considering that puzzles like this are a bit like early dementia tests. It's worth thinking what data gets collected when the world is asked to perform brainteasers to gain access to essential functions.