Измените

 

Warning: imagepng(/var/www/mojaopstina.rs/www-root/public/images/captcha/d261a45c8e3f9fb2c01df0b0472f46bd.png): failed to open stream: Permission denied in /var/www/mojaopstina.rs/www-root/library/Zend/Captcha/Image.php on line 563