Please note that CAPTCHA codes should be randomly generated and not reused to maintain security. The characters used in the code should be a mix of uppercase letters, lowercase letters, and numbers to make it challenging for bots to crack.
Remember that the purpose of CAPTCHA is to differentiate between humans and bots, preventing automated spam and abuse on websites. While the example above is simple, more complex CAPTCHA systems can include distorted characters, overlapping text, or even puzzles that require user interaction, making it even harder for bots to decipher.