Different Captcha at checkout for non-registered

Hello,

I have installed the reCaptcha for hikashop and it works at the checkout page for non-registered users,
but I don't like ReCaptcha.
I installed EasyCalcCheck+ and it works on the Joomla registration page, but not in hikashop.

I'm using Joomla 2.5.4
How can I integrate a more simple captcha or ECC+ in hikashop at checkout?
Should I code it somewhere in hikashop php files, what should I use?

Thanks in advance.