Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/18a2c6cbae0f31aedf72e9e5a71e5f70.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563