Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/9aa002ab0f3074d2c0378c1a53d18a20.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563