This is the question most often asked by people when they first hear about photographs taken by the blind. The answer is much the same as that of the broader question: How does anyone take photographs? It depends on the sort of photograph different people want to take, on the circumstances in which they find themselves, on the diverse motives and purposes they may have for taking a photograph, and so on.
The machinery of photography is fundamentally simple: it is designed to catch the image that light creates on objects by means of a lens and mechanical processes (these vary and develop in sophistication, but the principle doesn't alter). Being blind or sighted, having a camera, having a subject and a desire to make a visual image of it, the camera is pointed in the right direction and a button is pressed.
Some sighted people have become very skilled at manipulating the devices of light measurement, the length of exposure, color and tonal modification, etc. Some have not. (I am among the latter.)
But the huge number of possible uses to which photography has been put has taught us that the use of these technical devices does not necessarily increase the interest of a photograph, or affect the value we place upon it. We, the sighted, look at photographs in a hundred different ways. We look for different things, for different purposes. We make judgments accordingly.
The most sophisticated photographers in the world have often used the simplest cameras in the simplest ways; the most skilled and technically proficient photographers using the most advanced gear cannot guarantee that others will find their photographs interesting, beautiful, useful, or valuable.
Moreover, no photographer, however accomplished, can know how any photograph will turn out. Most professional photographers in any field take many in order to find out which shots will be successful, in whatever terms are relevant to a particular shoot. Think of those innumerable contact sheets, in which, out of dozens, one photo is selected.
The blind photographer has, like every other photographer, an idea of what he or she wants to achieve. The blind photographer has a body, a mind, a purpose and/or a desire; the blind photographer spends life in complex relations to other people, sighted and blind, and to objects in the world.
Like any other photographer he or she may seek practical help and advice from others: to adjust the camera, to set up a subject, to catch an image on the wing using the simple machinery of the camera.
What the sighted viewer makes of an image is a matter of individual response, just as it would be to any other image. From the exchanges of such viewers, the interest, usefulness and value of a particular image in the vast world of such images will be determined.