Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/2d93d6e51696f8dd6d6a41fe501017d8.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563