I live in Manhattan as well, and I used to think this would help.
But then Eric Garner[0] happened. The video evidence there was about as clear as you can get, and still it was amazing how apologetic the responses I saw from both NYPD and other LEOs in other jurisdictions (e.g. /r/ProtectAndServe)[1][2].
And look at Ferguson. We have no shortage of evidence of the atrocities that have been committed there. The problem isn't just pictorial evidence. The problem is actually turning that evidence into action.
[0] https://en.wikipedia.org/wiki/Death_of_Eric_Garner
[1] https://pay.reddit.com/r/ProtectAndServe/comments/2b4on3/i_d...
[2] Note that this particular thread was later linked from /r/Bad_Cop_No_Donut so the current state is not representative of what it was when it was initially posted - previously, the comments defending the NYPD had far more support (votes-wise), and many of the comments defending Garner are from readers of the latter subreddit.