Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/9ca66bd4b4d8e0dc293e559f1facc5ac.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563