OpenCaptcha

OpenCaptcha is an open source, free, public API that generates CAPTCHA images from text.

OpenCaptcha provides:

• A free, public API at api.opencaptcha.io.
• Documentation at opencaptcha.io.
• Self-hosting support (see the Installation section).

Usage

Example 1: Generated CAPTCHA images are randomly distorted.

curl -X 'POST' \
  'https://api.opencaptcha.io/captcha' \
  -H 'Content-Type: application/json' \
  -d '{ "text": "captcha" }'

Example 2: Generated CAPTCHA images can contain text in many languages.

curl -X 'POST' \
  'https://api.opencaptcha.io/captcha' \
  -H 'Content-Type: application/json' \
  -d '{ "text": "普通" }'

Example 3: Generated CAPTCHA images can be in a different colors

curl -X 'POST' \
  'https://api.opencaptcha.io/captcha' \
  -H 'Content-Type: application/json' \
  -d '{
    "text": "hello world",
    "theme": {
      "primaryColor": "#ADD8E6",
      "secondaryColor": "#FFFFFF"
    }
  }'

Installation

Option 1: Using Docker (recommended for self-hosting)

Requirements

• Docker

How to Run

1. From the root folder of the project, run the following commands:

   docker build -t opencaptcha -f ./src/Captcha.WebApi/Dockerfile .
   docker run -it -p 5280:8080 opencaptcha

2. The API can be accessed at http://localhost:5280.

Option 2: Using Visual Studio (recommended for development purposes)

Requirements

• Visual Studio 2022
  • With ASP.NET and web development installed from the Visual Studio Installer
• .NET 9 SDK

How to Run

1. Open the solution in Visual Studio 2022.
2. Build and launch the Captcha.WebApi project.
3. The API can be accessed at https://localhost:5280.

How to Test

1. Open the solution in Visual Studio 2022.
2. Run the tests in Test Explorer.

Acknowledgments

A significant portion of this project, especially the CAPTCHA generation code, is inspired by work originally published on February 9, 2004, by BrainJar.

Contributing

Pull requests are accepted.

License

MIT