First of all i hope someone can help me i do not know about php so if you can help me i apreciate it a lot if someone can give me the correct code to be added for the blow things

the below code is a captcha code i want to be able to set my own font how can i do this? and is it possible to turn this into a png image with transparancy background?

PHP Code:
//$text = rand(1000000,9999999); 
$text rand(10000,99999);
$_SESSION["vercode"] = $text;

$height 17;
$width 60;
$image_p imagecreate($width$height);
$black imagecolorallocate($image_p,243,247,250);
$white imagecolorallocate($image_p000);
$font_size 8;