The scratch-and-win specialist marks the keys with printed codes and covers them with a special scratch-off layer (thermochromatic or other security inks could be used).

刮奖专家以印好的编码作为标记，并在上面覆盖一层可以挂掉的特殊涂层（可以使用热变色油墨或其他安全油墨）。