Skip to content
[WIP] Libre Captcha framework
Java Scala Other
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


LibreCaptcha is a framework that allows developers to create their own CAPTCHAs. It allows developers to easily create new types of CAPTCHAs by defining a structure for them. Mundane details are handled by the framework itself. Details such as:

  • Background workers to render CAPTCHAs and to store them in a database
  • Providing an HTTP interface for serving CAPTCHAs
  • Managing secrets for the CAPTCHAs (tokens, expected answers, etc)
  • Safe re-impressions of CAPTCHA images (by creating unique tokens for every impression)
  • Sandboxed plugin architecture (To be done)

Some sample CAPTCHA generators are included in the distribution. We will continue adding more samples to the list. For quick deployments the samples themselves might be sufficient. Projects with more resources could create their own CAPTCHAs and use the samples as inspiration.

Why LibreCaptcha?

Eliminate dependency on a third-party

An open-source CAPTCHA framework will allow anyone to host their own CAPTCHA service and thus avoid dependencies on third-parties.

Respecting user privacy

A self-hosted service prevents user information from leaking to other parties.

More variety of CAPTCHAs

Ain't it boring to identify photos of buses, store-fronts and traffic signals? With LibreCaptcha, developers can create CAPTCHAs that suit their application and audience, with matching themes and looks.

And, the more the variety of CAPTCHAS, the harder it is for bots to crack CAPTCHAs.



FilterCaptcha Sample

An image of a random string of alphabets is created. Then a series of image filters that add effecs such as Smear, Diffuse, and Ripple are applied to the image to make it less readable.


RaindDrops Sample


An image of a word is blurred before being shown to the user.


An image that has a pair of words is created. The answer to one of the words is known and to that of the other is unknown. The user is tested on the known word, and their answer to the unknown word is recorded. If a sufficient number of users agree on their answer to the unknown word, it is transferred to the list of known words.


Things to do in the future:

  • Sandboxed plugin architecture
  • Audio CAPTCHA samples
  • Interactive CAPTCHA samples
You can’t perform that action at this time.