The “Captcha” idea is brilliant. While they are not totally foolproof (certain Universities have successfully been able to create software that are able to hack captchas), they provide a decent bit of protection from spam activity. The recaptha tool that many of us have seen on various sites on the web is a particular favourite of mine because apart from the added protection it also allows the crowd-sourcing of data via this small action. Currently I’ve seen two variations of this crowd sourcing. One to digitize books, so you’ll be shown a word that the Google OCR engine was probably not able to recognize and then you help them know what the word is, and the other one I’ve seen is the house numbers of Google Maps Streetview, which would probably give them more the ability to more accurately pinpoint addresses in their Maps. Below I’ve included two files that I’ve used to create a very basic captha module using PHP’s GD library. Continue reading How to create a Captcha with PHP GD library.