Ronald, if the version of your software is 1.5.3, you simply need to  comment the following string in /ow_system_plugins/base/init.php file:

$e->setData(new CaptchaField('captchaField'));

Hello i have 1.5.3 version and i have problem with captcha. I did everything, I commented out join.php, join_index.html and init.php and it is not working. When i am trying register i  get the message:

-Please, enter a valid usernameRequired

- Please, enter a valid email addressRequired

Pleas help me :)

Any help ???

pleas, pleas, pleasa, i need help where is support form this forum?

Davit, sorry, but it's not quite clear. You say that the problem is with the captcha, but you cannot register at your site because the username and email is required.
 
The message you are getting is related to your site settings. The profile questions you are talking about are required to be filled in. But it has nothing to do with the captcha image. If you have problem with the site settings submit your question to the General Questions forum and our support operators will be glad to assist you.
If you made some modifications and now your registration form stopped working - please specify what exactly you are trying to do and what exactly you've already done.
 
The more information you provide - the more details of the problem you will provide - the more effective our help will be.

I had a problem with captcha has stopped working. I wanted to turn it off as it was described in this topic. Captcha is off but now i have this problem. When i am trying register i  get the message:

-Please, enter a valid usernameRequired

- Please, enter a valid email addressRequired

I changed nothing in the script. Captcha stopped working after I turned off and now i have this the problem. I can't turn catpcha because it is not possible to register.

Davit, I suggest that you turn back the changes made for the captcha disabling and check if it solves the problem. If the problem disappears, please try to disable the captcha as I've described above once again, and if the problem occurs again, provide me with the screenshot of the code you change.

Ronald's issue with Captcha was solved by enabling FreeType extension of GD library ( enabled by hosting company).