provided by Star2Billing S.L.

This is the first time I tried to access the user signup page at http://mysite/A2Billing_UI/signup. Every field is fine except for verification image missing. I right click the image property, and found this:
http://mysiteA2Billing_UI/lib/captcha/captcha.php.

Is there anything wrong?

Added after 15 minutes:

Problem fixed.

I didn't install php-gd.

yum install php-gd fixed this problem.