Firstly historical background:
The phenomena of people witnessing atrocities and not acting predates photo taking. It is known as Diffusion of responsibility or Bystander effect. (1) The likelihood of an individual offering assistance or calling for help is inversely proportion to the number of people present in the group.
This phenomena can be attributed to the concepts of deindividuation (2) and victim blaming (3). Deindividuation is the notion that an individual loses their independent consciousness to a degree as being drawn into a group consciousness, that acting within a group, revokes all personal responsibility and accountability for actions or inactions.
Victim blaming is the propensity for people to blame the victims of violent crimes for somehow being complicit in bringing about the crime. By reckless behavior, perceived immoral conduct. This can the false comfort people seek as a protection, that it wouldn't happen to them, as such events are not part of chance, but rather have causal roots within the victim.
I believe the cause underlying this mentality runs deeper into the human psyche and taps into a primitive part of human nature that will form a subconscious alliance with the perceived stronger aggressor and so have less mercy towards the weaker victim. This is seen in more personal and extreme cases in the Stockholm Syndrome and on the coninuum of domestic violence. The following quote demonstrates this argument where the threat is real and present. I postulate this fear is underlying within many people's subconscious.
It is important to remember that Stockholm Syndrome develops subconsciously and on an involuntary basis. The strategy is a survival instinct that develops as an attempt to survive in a threatening and controlling environment. (4)
There has always been a voyeuristic nature to photography. (5)
The advent of internet communication, social media and the glut of social networking platforms have given rise to a popular form of communication, via the image. Pinterest being a good example. The availability of new technologies enabling people to take photos and upload instantly online, makes a tragic scene an tantalising opportunity for individuals to gain recognition online. Perhaps enhancing their perceived status or popularity, at the very least gaining them attention.
The psychology of the photographer:
This is a little researched area. I cannot find much on this topic, maybe somebody else can.
This book by Joel Morgovsky examines some of these issues (I am unable to quote further than the following):
While photographs are the most abundant image form in the world today, they are, at the same time, also the least carefully analyzed. Not one psychologist, to this writer’s knowledge, has attempted to apply relevant research on imagery and the creative process to the study of photographs as personal and cultural communications. Writers, painters, sculptors and scientists have served for years as illustrations of the creative personality, the creative process, and the creative product; photographers and photographs have not (Lindauer, 1977). (6)
It appears Joel Morgovsky has an interest in ongoing research into this:
According to Div. 1 (Society for General Psychology) member Joel Morgovsky, pictures aren't just windows through which we look out onto the world--they also serve as mirrors into the photographer's mind. (7)
(1) The Bystander Effect: A Lens for Understanding Patterns of Participation James M. Hudson & Amy S. Bruckman DOI:10.1207/s15327809jls1302_2
(2) Zimbardo, Phillip G. The Human Choice: Individuation, Reason, and Order Versus Deindividuation, Impulse, and Chaos, In W. T. Arnold and D. Levine (eds.), Nebraska symposium on Motiviation, Vol 17., 1969.
(3) Blaming the Victim and Exonerating the Perpetrator in Cases of Rape and Robbery: Is There a Double Standard? Steffen Bieneck, Barbara Krahé doi: 10.1177/0886260510372945
(4) Rainn.org Stockholm Syndrome Dr Joseph Carver
(5) Exposed: Voyeurism Surveillance and the camera since 1870 Sandra S Phillips and Simon Baker portrait.gov.au
(6) Noses on Our Faces: The Non-Use of Photography in Psychological Research and Practice
Joel Morgovsky DOI 10.1007/978-1-4684-1179-9_18
(7) American Pyschological Association Funding opportunities