The X-ray (Rontgen) is thrown from a fixed source into photodiodes. If there is an object between the thrown X-ray and the photodiodes, the rays penetrate the object and reach the opposite surface. The shape, type, and atomic weight of the object penetrated by X-rays are absorbed by photodiodes and reflected on the screen as an image. Depending on the quality of the X-Ray detector, the transmitted image may be either black or white, and colored images can be transferred at the higher segments. The object displayed on the monitor shows which atoms it contains according to the colored tones. 

Baggage machines use x rays to screen objects non-invasively.  X-ray inspection is commonly used for security screening of baggage, such as checked and carry-on luggage. The core system consists of an x-ray source, L shape photodetectors, and software. They’re used to build a picture of what’s inside baggage and allow security staff to check anything that looks suspicious. X-rays launched from one side of the machine are picked up by a pair of detectors on the opposite side. As your bag enters through the lead-lined curtains, it crosses the path of these X-rays and absorbs some of the energy they carry. This means that the X-rays that passed through the baggage have less energy than those that sailed straight past.