Prevent form spam by generating random, accessible arithmetic and logic questions.

Examples:

• "What is the fourth letter in snowboard?"
• "What is the sum of four and six?"
• "What is eight multiplied by two?"
• "Which is smallest: sixty-six, one hundred, or twenty-two?"

Users can respond with either the numeric or textual version of an answer (e.g. "16" or "sixteen").

For background info on this project, see my blog post: https://theodorejb.me/2012/12/30/responsive-captcha/

composer require theodorejb/responsive-captcha

1. Generate a random question:

   use function theodorejb\ResponsiveCaptcha\{randomQuestion, checkAnswer};
   
   $qa = randomQuestion();
   $realAnswer = $qa->getAnswer(); // save somewhere (e.g. in session or encrypted single-use token)

2. Display question in form:

   <label>
       <?= $qa->getQuestion() ?>
       <input type="text" name="captcha" />
   </label>

3. Check whether the user's response is correct:

   $answer = filter_input(INPUT_POST, "captcha");
   
   if ($answer !== null) {
       if (checkAnswer($answer, $realAnswer)) {
           // code to execute if the captcha answer is correct
       } else {
           // the answer is incorrect - show an error to the user
       }
   }