These photographs show different kinds of piercing, a type of body art which has a great number of followers, though not all so extreme.
Even if I'm not in contact with you, my readers, I am sure that most of you believe these images are true, as well as I myself believed they were true when I found them on the Net.
The question is: why do we believe them to be true? Furthermore: can we find an explanation which is not psychological, but logical?

To answer we must understand what an image is.

"In the General Registry Office only words existed, in the General Registry Office one could not see how faces had changed or how they were changing, while the most important thing would be just this, what time changes, and not the name, that never varies."
José Saramago, Todos os nomes, 1997, Torino: Einaudi, p.96 (my translation from Italian: original in Portuguese)

An image tells us something about a situation in a certain time and space:  time and space that can be fictitious, yet are represented IN the image. Images imitate perception, and perception is connected to time and space, is experience.
Charles Peirce (1839-1914), the founder of semiotics, called  the signs which direct us toward experience indexes. A footprint is an index: we interpret it as the effect of a cause.
Through of an index we are able to know  a cause by means of an effect. When we decide that an image is an index we bet that some real event has caused that image to possess such and such perceptive qualities.

Peirce said there is another kind of signs: icons. Icons let us know the object they represent because they share some property with it. An icon is similar to its object.
In thinking about images we usually stress the fact that they resemble the object. Actually, they possess perceptive qualities, and some of them are supposed to be those of the object, regardless of whether it is real or fictional. 

A photograph is an icon which is also an index: some of its perceptive qualities (some of the feelings I experience when I perceive it) are effects of an event which has happened in some place and time.

Thus, images are very different from synbols (the third kind of signs). A word is a symbol. A word is connected to its object by means of a convention. We often forget this characteristic of symbols, because to go from the expression to the content is a highly automatic process. We read "pizza" and we suddenly have the meaning of the word. But if I and you, my reader, decide that from now on, insted of "pizza", we will use the symbol XYX, we will understand each other all the same.
The symbol has no quality in common with the object, neither it is in any way its effect.

Thus, when we face an image,  we interpret its qualities, and organize them into a meaningful pattern according to rules of perception and cultural rules, but we also take a decision on the indexical character of the image. If we decide that the image is the effect of a cause, we establish a connection with some kind of empirical event. This is what happens when we look at the pictures of pierced genitals and say "Wow, you must be crazy to make such a hole in your cock!"  We take for granted that the image is true, that is, corresponds to a real event.

Now we come back to our question: why do we decide that an image is true?
First, the decision that an image represents empirical events is the result of an inferential process, that is, reasoning. Such a process is usually very fast and not conscious: the result comes to our mind as if it were obvious. I said 'usually': in some cases we have doubts. Then, we look more carefully at the image and try to take a decision. If we manage to do it, then we will think the image is true. Otherwise, we can go on without taking a  decision.

We can have external  or internal  reasons to decide that an image has indexical characters.
I will use the expression "is true" to mean such a property.

Most of the times we think that a photograph is true because another sign tells us so. This is an external reason. When we find a photograph on a newspaper, for instance, we think that it is true because we just trust that medium. In semiotics we say that a "trust contract"  is  established between two speakers when one of them believes the other's discourse,  not because she has proved the truth of  the discourse, but just on the basis of what is taking place in the communicational exchange. It can be a question of social role  (e.g.: the speaker is a policeman on duty, or a doctor); it can be a question of circumstance (e.g.: Alvin has just asked Burt the direction. Alvin does not know the town: he must trust Burt); it can be a question of paratext (by paratext we mean what stands 'around' the text: the book cover, the title of a movie that defines it as a documentary, and so on) (e.g.: the CNN logo that marks the images as reports). These are external reasons.

The internal reasons that make us believe an image is true must be part of the text. Of course no text can be interpreted without some background knowledge, and images make no exception. An image like this

can be difficult to interpret for a boy who has never seen female genitalia. The boy might be able to understand that the photograph represents some  part of a human body and, if he has some verbal information, he can easily understand which one. However, if it is the first cunt he sees, this particular one will supply him with the general idea of all the cunts, that is, the concept.
Images, however, are different from symbols because they are individual, while symbols directly refer to concepts. The difference is crucial.
Let's take the following verbal description: "a beautiful black woman".
Try to compose this image in your mind. First, think that you can do it because you can read English.
When you have an image in your mind, click HERE.