Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/88c8d0cc5d0f0a56dcd9c05fc2b6361a.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563