Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/b66e02abf2449e1e4e6a1e2a4ba0ba53.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563