Tatoos are permanent patterns or images drawn into the skin using ink or some other pigment. The ink is placed under the skin so as the make it permanent. The procedure is known in medical terms as micro-pigment implantation. Tattoos are also considered a type of body modification.
For these reasons, tattoos can be very difficult to remove. In fact, until relatively recently it was impossible to remove a tattoo. Today there are a number of cosmetic surgical techniques that can be used to completely or partially remove a tattoo. The most common method is to use laser. The procedure is not perfect however, it is very expensive and can leave badly blemished skin.

Green based inks are the most difficult to remove. There are also some shades of black, and homemade tattoos that simply cannot be removed.
The older way of removing tattoos was to use hydrogen peroxide. This was loaded into the tattoo machine and the image was retraced wit the chemical.