Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/6a63098cb3e5ef0a3afa6a3b0baa94ec.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563