Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/be7c4e9f8e32fa7a9b2ffb083122e8ff.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563