Not entirely sure about the NY Legal System
But surely, the information sent in will not be enough to convict somebody of any crime without any other evidence, as it can be tainted. With other evidence it is corroborating information that strengthens the Police's argument.
Any decent lawyer will be able to determine if the case is based entirely upon the photo/video evidence, and can debunk it as potentially "shopped". If enough evidence exists to prove the guilt of an individual, then even if a piece of evidence is tainted, it can be dismissed, and the remaining evidence stands on it's own merit. If you have enough evidence to prove someone's guilt, then the District Attorney would be foolish to bring up" taintable" evidence in court.
In short, Photo's and Videos from unknown sources are useful in the investigative stage of the process. That is all.