system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What is it that makes it so computers can't solve captchas?
gpt
It requires image recognition capabilities that don't yet exist outside some advanced machine learning laboratories. 

Asking a computer to look at a cluttered image of a street corner and identify a fire hydrant is not something it is going to be able to do unless it's had a lot of practice identifying fire hydrants from multiple angles, zoom, color, etc. 

Humans are able to solve them because we process things differently. We can look at that image and process that fire hydrant, based on prior knowledge of what a fire hydrant looks like.