CaptchaMixer

CaptchaMixer is a CAPTCHA image generation engine for .NET.

CAPTCHA generation algorithm is described as a pipeline consisting of vector and raster processors. Processors and vector/raster image layers may be mixed in various ways to compose unique and completely differently looking CAPTCHA images.

Key features:

• Well-packed: comes with dozens of vector and raster processors to start creating CAPTCHAs with
• Simple visual randomization: processors consume library's own ValueProviders instead of plain values, and the static ValueProviderFactory helps even more by providing numerous shorthand methods
• Extensibility: add your own vector and raster processors by implementing trivial interfaces and/or by using various base classes and helper methods
• Templates support: take out generation pipeline parts or even complete pipelines into ICaptchaMixerTemplates to easily reuse them
• Development facilitation: use the CaptchaMixerDebugBuilder to preview how your images are being built step by step
• For math lovers: the VectorMath static class with vector utility methods (Bezier curves, lines, points etc.)
• Cross-platform: thanks to SkiaSharp under the hood
• Well-documented: most library's APIs are augmented by detailed code documentation

Philosophy

The library is not bundled with ready-to-use CAPTCHA templates.

It is implied that you will create your own templates.

There are a couple of text-image templates in CaptchaMixer.Examples project, but they are, well, examples. We believe that for sake of better security CAPTCHA templates shall not be open-sourced.

See security considerations for more details and recommendations.

Examples of what you can achieve

These are proprietary Kaspersky templates, they are not included.

But that is what we've managed to do for our needs using stock processors only. So you can do something similar or even better.

Further reading

• Getting started - creating your first CAPTCHA
• CAPTCHA anatomy - image generation pipeline and layers structure
• Processors - out-of-the-box processors and implementing your own
• Value providers - randomizing and otherwise controlling behavior of processors and image generation pipelines
• Templates - using templates
• Performance and multithreading
• Security considerations - automated recognition precaution and general recommendations on using CAPTCHAs
• Building - guide on building the solution for contributors