[sanswork]

The only proof you have that it IS evidence is the word of someone who you know is willing to break the rules to secure a conviction.

[dagw]

Sure, and that is an argument you can make in court after the evidence has been submitted.

[hasenj]

I thought an evidence was an objective piece of data, not someone's word.

[bzbarsky]

An objective piece of data like what? A digital photo? A network traffic log? A printed photograph? A phone call recording?

These are _all_ based on someone's word, in a world of Photoshop, text editors, hex editors, scanners and printers, voice synthesis, etc.