The captcha in the application uses GD2 and should not be an issue since most all PHP functions nowadays have GD2.
There are so many reasons why you should upgrade from such an old version. You do not buy 8.12 you simply renew your members access for 39.00 and you can download the latest. There are lots of security fixes and enhancements that are there you want. In fact 8.2 which should be out soon is going to include the new plugin system we designed that allows you to write your own plugins banner ads content and stick it into various places which will make upgrading a snap in the future.
Supporting Imagemagick with captcha is something we might do in the future the issue is there are different libraries needed for imagemagick to handle captcha whereas GD2 does it by default. Most people using vb
and captcha end up using GD2 because they can not get imagemagick to do it right.