Now that the system has gone digital the question of physical links has been put aside. All that is required to authenticate a crime picture is that some breathing and conscious human being has to get into the witness box and swear "Yep, that's the way it was." The crime scene picture has passed in substance from being evidence to becoming mere testimony.
Maris:
Photographs in Canadian law (and British law before that) have always been considered as demonstrative, rather than direct evidence.
They have always required confirmation from people who could testify to their accuracy as representations of reality.
The only exceptions were those photographs that revealed what people could not or did not naturally observe. Photographs like micro-photography and automatic surveillance or traffic cameras.
Those latter types of photographs did require testimony that corroborated the fact that they had not been manipulated.
The analogue photography process helps supply that corroboration, but it doesn't definitively establish it.
The strength of photography, when it comes to evidence, lies in its persuasive and revelatory abilities. Choice of an analogue workflow helps corroborate the accuracy of the results, but it doesn't legally establish them.
There are some exceptions prescribed by statute. They tend to be related to things like microfilm copies of historical records.
