Fatal error: Call to undefined function imagettfbbox()

On the following url:

http://teamhillman.co.uk/customer_service.php

Im getting the following error:

Fatal error: Call to undefined function imagettfbbox() in /home/martin/public_html/includes/functions/func_captcha.inc.php on line 50

Make sure you have the GD2 and FreeType PHP extensions installed/enabled. GD2 is also required for creating thumbnails.

http://www.php.net/manual/en/function.imagettfbbox.php
""This function requires both the GD library and the » FreeType library.""

I have installed both GF and Free Type.

All is now working.

thanks

Where and how do i install this ?

http://stackoverflow.com/questions/21216129/install-gd-library-and-freetype-on-linux