Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/1b0e7b6706ebccd7f557b14c9c2c0920.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563