Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f6a1d0b48001fc9ccfa7f883437f4d8d.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563