To verify that you are indeed a human, most websites and applications use a simple test. Here’s how it works:
When prompted to confirm you’re a human, look for the reference ID displayed on your screen. This unique code is assigned to you by the website or app.
Press and hold the number corresponding to the reference ID (in this case, 35a10ad9-6c10-11f0-bd70-45b6799a10eb) as long as it’s lit up on your screen. This indicates that you’re interacting with a human interface.
Release the key or press enter when prompted to confirm your action. If everything goes smoothly, the website or app will recognize your input and acknowledge that you are indeed a human.
This multi-step verification process helps prevent automated software from impersonating humans and abusing online services.
Source: https://www.sfchronicle.com/sf/article/delta-pilot-arrested-sfo-20788655.php