X-ray baggage scanners play an important part in ensuring safety by assisting operators in detecting smuggled or hidden contraband and ensuring explosives, weapons, narcotics or weapons of mass destruction are detected before damage or harm occurs.
Since different materials absorb X-ray at different levels, the image on the monitor lets the machine operator see distinct items inside your bag. Items are typically colored on the display monitor, based on the range of energy that passes through the object, to represent one four categories: Organic, Inorganic, mixed materials and metals.
While you are stepping through the metal detector, your items go through the X-ray system. X-rays are like light in that they are electromagnetic waves, but they are more energetic, so they can penetrate many materials.