regular expression for an image verification

Hi
I have created about a dozen different images for a image verification section on a website, each containing six letters or numbers.They randomly change when you refresh the page.I need a regular expression to validate each user input for each individual image.

thanks

 

why regex? get a good function captcha script, how more advanced the better is the protection! and mostly free of charge!

 

That's an awful way of doing verification, use a proper Captcha script, or if you're lazy use something like Recaptcha.