Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cf51bc24c9f6e24eeb0d361e3a751e1a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563