Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/39f0b2b0002b315f89f1eff2a8d79d72.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563