Although videos and photographs offer the possibility of being extremely useful as evidence in legal cases, there are both procedural and material issues concerning their use. Also, they can be easily used to manipulate the emotions of a jury.
The first has to do with chain of custody. Although a photograph of a crime scene taken by an official photographer can be reliable, something like a photo on a cell phone taken by a spectator may well have been manipulated. Even with meticulous preservation of metadata, it can be difficult to tell if an image has been manipulated. moreover, a skilled photographer can use lens choice and camera angle to create misleading images.
Finally, visual imagery can often produce strong emotional effects that can warp the emotions of a jury and skew outcomes.