In practice there are some difficulties with this technique: wet and dry fingers make very different images, and the system is sensitive to dust and dirt on the surface. The unit is large and expensive. This system is also easy to cheat and if the skin is damaged, the fingerprint is not recognized correctly. The recognition of the fingerprint of older people is also difficult to do because their skin may not be elastic enough. In some circumstances this may result in false recognition. If the stored fingerprint was taken with less pressure, false acceptances may occur.