Not all tattoos are the same. Not only according to how they look but how they came to be and why.
Traumatic tattoos appear against the will of the one who wears it. They occur when a powder of some type enters the wound and stays there permanently. Coal miners can get tattoos of this kind when a coal dust enters the wound that they receive while underground. Gunpowder from fired weapon can produce the same effect if a person that fires a gun has a wound on a hand. Asphalt from the road can make a traumatic tattoo to a person which experienced an accident and have been sliding on the road with exposed skin. Amalgam tattoo can occur during the dental treatment and accidental stabbing with a pencil or pen can leave graphite or ink under the skin. They are hard to remove.
Cosmetic tattoo (or permanent makeup) is a tattoo designed to look like a classical makeup. It is done on lips, face, eyebrows and eyelids. It is done to remove necessity of putting on makeup every day or to hide imperfections resulting from nature or some illness. It is also used to hide surgical scars from mastectomy and as a replacement for missing breast's areola.
Medical tattoo is one name for few different tattoos. Some medical tattoos are notifications that a patient suffers from a chronic disease or allergy that, if hits, renders patient unable to speak and inform others of his ailment. Medical tattoos can replace army dog tags and contain info about blood type for instance. Tattoos are used in radiology as a targeting aid to show a place where the beam should be pointed. Without it irradiated field would be too large and could damage surrounding tissue. Medical tattoos were used in Ice Age and in Ancient Egypt as a form of acupuncture.
Tattoos for identification were and are used as a positive or negative identification. Ancient tribes had each their own tattoos which showed lineage, social position, and status within the tribe. Criminals and deserters were tattooed as a form of punishment and to prevent escaping. Inmates in Nazi concentration camps during The Holocaust were tattooed with numbers on their hand in order to be identified when they are dead. Roman soldiers of the Roman Empire had identifying tattoos on their hands which prevented them from deserting (or at least made it difficult).
Amateur and professional tattoos are today the most widespread types of tattoos. Amateur tattoos are usually made in one color and their ink is in the top layer of the skin. This name refers to tattoos made by amateurs which are just training the trade and for tribal tattoos that are rites of passage, symbols of bravery or beauty. Professional tattoos are often done in more colors with professional tools and in deeper layers of skin which makes tattoo of better quality.
Other types of tattoos are corneal tattoo (tattooed eyeball), palate tattoo (a tattoo place inside ones mouth – on the palate), tongue tattoo (does what it says on the tin), inside lip tattoos, teeth tattoo (tattoos on pulled out teeth), glow-in-the-dark tattoos and blacklight tattoos which glow in the dark and under the UV light, hair tattoo (tattoo on a bold head that looks like a very short hair), and tattooing on animals like pigs and cats (we don't know why...).