[TYPO3] Image is blank when using CAPTCHA with frontend

[Alex Hobbs]

> http://www.bigroo.com/typo3/ext/captcha/captcha/captcha.php

Hi Christopher, oddly enough this file is now working, I don't know
what changed there. So that's great!

But...the session variable:

$captchaStr = $_SESSION['tx_captcha_string'];

is blank when the form is submitted (ie it's blocking the mysq insert
query regardless of the $tipData['captchaResponse'] value (which posts
okay).

Where should I set the session_start() command in
class.tx_fertenews_pi1.php so that the tx_captcha_string set in
captcha.php is retreived?

Thanks in advance,
Alex.