Apologies if i have posted this in the wrong place but i am kinda new to this forum.

I am running a captcha contact form, which has been running fine, however recently the captcha image within the form does now not appear and i am struggling to work out why.

I am fairly new to this process and have tried to research into what the problem may be but without much success.

The error that i am getting is as follows:-
Fatal error: Call to undefined function imagettfbbox() in /home/public_html/Captcha.php on line 60

Line 60 in my Captcha.php file is as follows:-

$textbox = imagettfbbox($font_size, 0, $font, $code);
$x = ($image_width - $textbox[4])/2;
$y = ($image_height - $textbox[5])/2;
imagettftext($image, $font_size, 0, $x, $y, $text_color, $font , $code);

What i don't understand is that the script has been working fine without any changes in code or directory. I am fairly new to this so am stuck for ideas.

My full code for captcha.php is included as attachment.

Thanks in advance!