Evolution of Ctrip's Graphical Captcha Service: From 1.0 to 2.0
This article recounts the development of Ctrip's graphical captcha system, describing its early .NET‑based implementation, the challenges encountered such as uniform difficulty, limited data collection, and poor user experience, and how successive redesigns—including multilingual support, adaptive difficulty, and slider‑plus‑character selection—balanced security and usability.
