README

Admin image CAPTCHA enhancement for Magento 2: optional per-character colors and grayscale noise for better readability on the backend login (and other admin forms that use the default image CAPTCHA). Storefront CAPTCHA is unchanged.

• License: MIT — see LICENSE.txt.

Requirements

• Magento 2.4.x (Open Source or Adobe Commerce) with Magento_Captcha enabled
• PHP 8.x (match your Magento installation)
• GD extension with FreeType (imagefttext) support (same as core image CAPTCHA)

Installation

Option A — app/code (typical)

1. Ensure the module lives at:

   app/code/XavierSanz/ColorCaptcha/

2. Enable the module and update the database:

   bin/magento module:enable XavierSanz_ColorCaptcha
   bin/magento setup:upgrade

3. Recompile DI (production mode) and flush caches:

   bin/magento setup:di:compile
   bin/magento cache:flush

Option B — Composer (path repository)

The package name is xsanz/magento2-module-admin-color-captcha (see composer.json). In the Magento project composer.json, add a path repository pointing at this directory, then:

composer require xsanz/magento2-module-admin-color-captcha:^1.0
bin/magento module:enable XavierSanz_ColorCaptcha
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento cache:flush

Adjust the version constraint if you tag releases (e.g. ^1.0).

How to use

1. Turn on admin CAPTCHA (core)

Per-character colors only apply when Admin CAPTCHA is enabled.

1. In the Admin, go to Stores → Configuration.
2. Open Advanced → Admin → CAPTCHA.
3. Set Enable CAPTCHA in Admin to Yes and configure forms, mode, and attempts as needed.

2. Enable per-character color mode (this module)

In the same section (Advanced → Admin → CAPTCHA), below the standard fields:

1. Set Enable Per-Character Color CAPTCHA to Yes.
2. Optionally adjust Text luminance and Noise luminance fields (all are 0–255, BT.601 luminance).

Defaults (from etc/config.xml, restorable via Use Default in the UI):

Keep text luminance max clearly below noise luminance min so letters stay darker than the noise.

3. When you will see it

Admin CAPTCHA appears according to your Displaying Mode (e.g. after failed login attempts). Refresh the CAPTCHA image with the reload control next to the image if needed.

Behavior notes

• Admin only: The module replaces Magento\Captcha\Model\DefaultModel only in the adminhtml area. Customer-facing CAPTCHA is not affected.
• With the feature off: Behavior matches core (single-color Laminas image pipeline).
• With the feature on: Each character is drawn in a random color within the text luminance bounds; noise is grayscale only; distortion uses an RGB-preserving resample so colors remain visible after the wave transform.

Configuration scope

The CAPTCHA group is available per website scope in Configuration. If you use multiple websites, set values under the scope where you manage admin settings (often Default Config).

Uninstall

bin/magento module:disable XavierSanz_ColorCaptcha
bin/magento setup:upgrade
bin/magento setup:di:compile
bin/magento cache:flush

Remove the module files if you no longer need them. Config keys under admin/captcha/* for this module may remain in the core_config_data table until cleaned up manually if required.

Support

Issues and improvements: maintain in your project or VCS as appropriate for XavierSanz_ColorCaptcha.