Modern captchas rarely rely on the puzzle alone. They score the visit first, using the IP address, the browser and the behaviour, and show a puzzle only when the score is doubtful. A trusted visitor often passes without seeing anything.
Seeing many captchas is a sign the site distrusts your address or your browser. A better address type lowers the number; so does slowing down. When a captcha is solved, the result is a token, and many sites accept it only from the address it was solved on.
Read next: Why captcha tokens fail