Friendly, easy, lightweight, self-hostable CAPTCHA service. https://captcheck.netsyms.com
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readme.md

Captcheck

Easy, light, self-hostable CAPTCHA service. Works on all modern browsers and IE9+. Uses icons from Font-Awesome.

How to use

In your form, put an empty div with the ID “captcheck_container”. Add captcheck.js into your page.

<!DOCTYPE html>
<html>
    <head>
        <title>Captcheck Sample Form</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <script src="captcheck.js"></script>
    </head>
    <body>
        <form action="submit.php">
            <input type="text" name="form_field" placeholder="Some random form field" />
            <div id="captcheck_container">
            </div>
            <button type="submit">Submit Form</button>
        </form>
    </body>
</html>

When the form is submitted, your server will receive two extra form fields: captcheck_session_code and captcheck_selected_answer. In your form handling code, send a request to http(s)://captcheck-url/api.php. Pass the variables session_id and answer_id with the values sent with the form, and also pass the variable action with the value verify.
You will receive a JSON response with (among other things) "result": true or "result": false. If result is false, the user failed the test, and another variable msg is available with an explanation.

Example URL:
http(s)://captcheck-url/api.php?action=verify&session_id=<captcheck_session_code>&answer_id=<captcheck_selected_answer>

Example responses:
{"session":"some_session_id","result":true}
{"session":"some_session_id","result":false,"msg":"Answer incorrect."}

Installation

  1. Run composer install.
  2. Copy settings.template.php to settings.php and plug in your settings.
  3. Install the database.
  4. Customize captcheck.js with the correct api_url.
  5. Follow the How to Use section and the example setup in test.html and test.php.

Execution Flow

JS = captcheck.js, API = api.php, FORM = parent form, 
SITE = form processing code, -> = some action taken on the right by the left

JS -> API:      Request session ID, question, and answers (with scrambled random codes)
API -> JS:      Sends info, saves session ID, correct answer, and scrambled answer codes in DB
JS -> API:      Requests answer images by sending scrambled value and session ID
JS -> FORM:     Adds hidden field with value=session ID, displays question and images
[USER SUBMITS FORM]
SITE -> API:    Sends session ID and scrambled answer
API -> SITE:    Responds with true/false to indicate if the answer is valid, marks session as expired to prevent CAPTCHA reuse