Something simple

I want to make an online game, using php. I want to allow users to sing up very fast, but also prevent automatic registrations. So, I have to use pictures, where a code has to be written in a textbox. I wrote the script for generating photos. How do I have to do now to memorate the codes on the server, but to prevent automatic processes, delete them after a period of time. I mean that a user creates an acount using username password, that code (and optionally an email adress). Probably that requires operations with ip.

Usually, how it’s done?

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