Aren't you just suggesting a very simple CAPTCHA challenge? This is an area that has seen an arms race for over a decade of platforms coming up with increasingl

Aren't you just suggesting a very simple CAPTCHA challenge? This is an area that has seen an arms race for over a decade of platforms coming up with increasingly complex "human-intelligence" challenges, and botmasters coming up with increasingly ingenious ways to bypass them (including, sometimes, using real human intelligence)