Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/f3a89fc894a5fa4a2fc1edb2f1c9c8a3.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563