Custom Captcha Field for Fluent Forms

Adds a "Custom Captcha" field to the Fluent Forms editor with three challenge types:

• Image captcha — a 6-character code rendered as an image, with customizable text color and a transparent background by default so it blends with any form design
• Math captcha — a simple arithmetic question rendered as an image
• Question and answer — you define the question (field label) and the expected answer

Challenges are single-use and expire after 15 minutes. Answers are stored server-side via WordPress transients — nothing is exposed to the browser except the image itself. Visitors get a refresh button to request a new challenge, and the captcha automatically renews after each AJAX submission, so it also works on cached pages. On top of the captcha you get two extra spam defenses:

• Time-trap (optional, off by default) — submissions completed faster than a human possibly could are rejected via an HMAC-signed timestamp; enable it and set the minimum submit time per field
• Disposable email blocking (optional, on by default) — rejects submissions where an email field uses a temporary/disposable email domain like mailinator.com or yopmail.com; extend the list with the ffc_captcha_blocked_email_domains filter

Everything runs on your own server: no external captcha service, no API keys, no cookies, no visitor data sent anywhere.

2.0.0

• Security: challenge answers are no longer stored in a publicly readable file; each challenge is now a single-use, expiring token stored via WordPress transients
• Security: removed eval() from math captcha validation
• Added: transparent captcha background (new default) and customizable text/background colors
• Added: refresh button on the captcha image
• Added: captcha auto-renews after AJAX submissions and on page load, so it works with page caching
• Added: optional time-trap — reject submissions completed faster than a configurable minimum (default 3 seconds) or carrying a tampered timestamp
• Added: optional disposable email blocking for the whole form (filterable via ffc_captcha_blocked_email_domains)
• Fixed: compatible with Fluent Forms 5+ hook names (validation no longer relies on a deprecated hook)
• Fixed: math challenges no longer produce negative answers
• Fixed: text captcha comparison is now trimmed and case-insensitive
• Fixed: field renamed from "Recaptcha" to "Custom Captcha" (this plugin is not related to Google reCAPTCHA)

1.0.0

• Initial release