Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/31d22f0f1d9a9d751d5d0a07657aad9b.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563