This plugin hasn’t been tested with the latest 3 major releases of WordPress. It may no longer be maintained or supported and may have compatibility issues when used with more recent versions of WordPress.



MetaCaptcha uses the proof-of-work (or “client puzzle”) approach for combating spam. Proof-of-work approaches slow down spammers by requiring them to solve computational puzzles before accessing a desired service. The idea is to impose a per-access cost in hopes of reducing abuse. More specifically, the cost to spammers will be computational resources that they devote to solving a puzzle before sending each message. The approach was first outlined by Dwork and Naor. However, Laurie and Clayton demonstrated that a small constant cost would fail to significantly reduce spam and a large one would burden legitimate users. Later, Liu and Camp demonstrated that if puzzle difficulties were based on user reputations then a proof-of-work approach would indeed be successful. Thus, malicious clients (spammers) would need to be issued “harder” (longer to solve) puzzles than non- malicious clients. The new comments on your blog will be sent to our MetaCAPTCHA server for spam classification.


  1. Upload folder metacaptcha to the /wp-content/plugins/ directory
  2. Activate the plugin through the ‘Plugins’ menu in WordPress
  3. Register an account at and get the PRIVATE_KEY and PUBLIC_ID. Replace your PRIVATE_KEY and PUBLIC_ID at line 3 and 4 of metacaptcha_lib.php
  4. Done

Contributors & Developers

“MetaCAPTCHA” is open source software. The following people have contributed to this plugin.

Translate “MetaCAPTCHA” into your language.

Interested in development?

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  • Add useful computation fishy
  • Add exchange shared secret key


  • Fix readme.txt


  • Fix readme.txt
  • Simplify the cookies model
  • Storing local score and timestamp


  • Update code so it can work with MetaCAPTCHA protocol located on
  • Reload page after verifying cookies complete