Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/cda9fbf497a7c3218e9b30cd6c1a6bd3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563