The Identity Masks are made from nanotechnology that uses photonic displacement to bend light around the wearer to appear like whoever you want. Aliens, particularly the DNAliens and undercover plumbers, use them to blend in with their surroundings. They do not require any previous training as Ben could use it effectively to blend in with DNAliens. They can easily be taken off so they aren't grafted to the skin like the Omnitrix. The false image that it creates can be disturbed by sudden flashes of light such as lightning.