Documentary photography usually refers to a type of professional photojournalism , but it may also be an amateur or student pursuit. The photographer attempts to produce truthful, objective, and usually candid photography of a particular subject, most often pictures of people. The pictures usually depict a certain perspective of the photographer.
“Usually such photographs are meant for publication, but are sometimes only for exhibition in an art gallery or other public forum. Sometimes an organization or company will commission documentary photography of its activities, but the pictures will only be for its private archives.” 
when shooting documentary photography it is important to have an angle, and work towards an overall or theme.
“For me, documentary photography has always come with great responsibility. Not just to tell the story honestly and with empathy, but also to make sure the right people hear it. When you photograph somebody who is in pain or discomfort, they trust you to make sure the images will act as their advocate.” 
Photographer Ed Kashi is well known for his work surrounding humanitarianism.
These images were taken from his work on northern Nigeria, done for National Geographic in 2013. As you can see they depict a place and its culture, in essence relaying a story to the viewer. The photographer is likely to choose their shots carefully in order to paint the picture they are trying to portray and create an overall piece that works towards a theme.
These pictures are taken from a collection titled cocaine blues by photographer Eugene Richards.
As you can see these photos document the gritty life styles of drug abusers, giving the viewer an insight into their world. Documentary Photographers often get close to the people they are photographing in order to get a true representation of their world.
“It’s a process of getting to know people. That’s what photography is to me. It’s about paying attention, not screwing up and blowing a great opportunity.” 
 Unknown – Definition Of Documentary – Unknown – http://documentaryshooters.com/definition-of-documentary – 04/05/2014
 Giles Dudley – Unknown
 Eugene Richards – Unknown
http://photoquotations.com/a/569/Eugene+Richards (Eugene Richards)