Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/d171a3e3b9cbe5dbd34e74f524e9d3a6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563