Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/d5b6fb69f15a7d5ac2758744d464d0c1.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563