Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/5bc3f89e2cf1a3402f9d9511b34ae1f6.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563