The article discusses the concept of CAPTCHAs, which are tests designed to distinguish between humans and computers. CAPTCHAs are used to prevent automated systems from performing tasks such as signing up for email accounts or accessing certain web services. The authors provide examples of different types of CAPTCHAs, including GIMPY, BONGO, PIX, and ECO, each designed to challenge computers while being easy for humans to pass. They also explain the importance of making CAPTCHA code public to ensure security and to encourage the development of new AI solutions. The article highlights the challenges and limitations of CAPTCHAs, such as the issue of "stealing cycles from humans," where malicious programs use human users to solve CAPTCHAs. Additionally, it explores the broader implications of CAPTCHAs in various applications, including free email services, search engine bots, and shopping agents. The authors acknowledge the contributions of various researchers and organizations in developing and refining the concept of CAPTCHAs.The article discusses the concept of CAPTCHAs, which are tests designed to distinguish between humans and computers. CAPTCHAs are used to prevent automated systems from performing tasks such as signing up for email accounts or accessing certain web services. The authors provide examples of different types of CAPTCHAs, including GIMPY, BONGO, PIX, and ECO, each designed to challenge computers while being easy for humans to pass. They also explain the importance of making CAPTCHA code public to ensure security and to encourage the development of new AI solutions. The article highlights the challenges and limitations of CAPTCHAs, such as the issue of "stealing cycles from humans," where malicious programs use human users to solve CAPTCHAs. Additionally, it explores the broader implications of CAPTCHAs in various applications, including free email services, search engine bots, and shopping agents. The authors acknowledge the contributions of various researchers and organizations in developing and refining the concept of CAPTCHAs.