what role can photographs play in revealing injustice? What role can they play in encouraging people to take action against injustice?

I've never had a photography class, so I'm basing my answer off of what I know and my own logic. So, I believe photographs, when it comes to justice, can show who did what, especially if the photograph was of catching somebody in the act of a crime. Take security cameras at stores and banks, for example, as even though they are not photographs and just video evidence, it can catch a robbery in the making, which they may even be able to the person's face, which can be evidence to arrest the person and for the bank/store/etc. to achieve justice. This can cause people to perhaps stop doing crimes, as they can easily be caught in the act. Also, it may persuade people to set up cameras or take photos if they feel like something may happen to have evidence of the situation.

Hope I helped.