When used on humans, it can penetrate the skin, and tissues; but not bone. To start off, these rays are invisible to our eyes, are more active than light photons. They are produced by allowing an electric current to pass through a vacuum tube. They can go through soft material such as skin but are stopped when they reach things like bones, tumours, metal objects etc. and will accumulate in these dense objects which will provide an image. The X-ray radiation act in a very similar fashion to light parcels, the more rays that are absorbed in a dense object, the clearer the picture will be.

X-rays are in many ways, very similar to visible light and light rays. Both are types of electromagnetic energy that is wavelike. The X-rays which are carried by particles called photons. The difference between the X-rays and visible light rays are the wavelengths of the rats which are also expressed as the energy level of the individual photons.
Visible light photons and X-ray photons are both created by the movement of electrons in atoms. When an electron drops to a lower electron shell or orbital, it needs to release some energy: therefore, it releases the excess energy in the form of a photon. The energy level of the photon varies and depends on how far the electron dropped or raised between shells.
Light photons are absorbed very well by the atoms in your body tissue. On the other side, radio waves don’t have enough energy to move electrons, so they just pass through most materials. However, X-ray photons have too much energy also allowing them to pass through most things.

When Wilhelm Conrad Roentgen ( the founder of the X-ray ) first discovered the X-ray by accident, he took the first picture of an X-ray to examine his wife's hand. The dark part in her hand is the ring, it is obviously the darkest object in the crude picture because gold is fairly denser than bone..