By now you would be used to entering the text for an image like this:
The idea is this will prevent bots because only a real user can interpret the image.
However this is not an obstacle for a determined scraper because of services like deathbycaptcha that will solve the CAPTCHA for you. These services use cheap labor to manually interpret the images and send the result back through an API.
CAPTCHA's are still useful because they deter most bots. However they can not prevent a determined scraper and are annoying to genuine users.