Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6841afd74e8d8d304092f71bf2e6c6e3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563