i have a problem in the comments system the captcha dos'nt show and instead is written security image

i know the first thing to do is to look in the forum .and i search and look but... all the answer i found wasn't written in a language i can

understand... i new to joomla (only from today) and to the wed subject in general( i installed apache yesterday)

i am working in localhost.. everyone is talking about permission setting.. i don't know what that is or where to do it in local host?

can anyone please write what to to but in a language that a beginner (not only to joomla but to the web)will understand ????