@Joe Hylkema
Worse than arse, actually.
All the Polaroid snaps I've ever seen have had foul colour fidelity ("No, I am NOT that fucking shade of green!")
They were OK for those applications where (like the ambos or on a film set to assist in continuity between takes) the important part was the content of the shot (trashed vehicle, relative locations of props and actors) not how photorealistic it was.
And they're OK for "arty shots" as referenced above, but as a "serious camera" they are a fucking joke. There are far superior cameras and film stocks than the Polaroid and its instant processing film. The only advantage to a Polaroid was the "you don't have to wait 7 days" (as it was back then before 24-hour and (much later) 1-hour processing).
Now, the resolution on even the inexpensive digital cameras these days is such that they surpass most mass-market film stock (modern digital video "handycams" are broadcast quality, something the old "Super-8" film stock and later mini-VHS handycams never were). And that's before you get into the more expensive digital SLRs with the capacity to use the same selection of lenses and filters as the (vastly-superior-to-Polaroid-in-every-way-except-speed-of-processing) professional film cameras and the added advantages of superior resolution and the ability to upload to the net at the nearest Cybercafe.
Film is going the way of the Dodo, it is only fitting that the crappiest film stock should be the first to go.
As to replacing it for the ambos: A portable memory-card-capable printer in the back of the ambulance would probably do quite well - I'm sure it could spew out all the relevant pics of the crash scene on the trip between scene and hospital - and the trashed car will only look green if it was actually painted green.
As to digital being "alterable", yes it is - for a *competent* digital artist. Just as film stock has been alterable by competent photographers for years.
Incompetent artists/photographers are not going to convince anyone, irrespective of the medium. Despite what the average PHB might think, you can't just "Photoshop this image to make it show my rival committed the murder" with ease. We have not yet got "You have opted to replace person 1 in image A with person 3 from image B. Please click OK to continue..."
The Photoshop tools are digital equivalents - cut, paste, draw, airbrush, smudge etc - of real tools used for years by film photographers - but you've still got to know how to use them properly.
And the same methods of detection (and probably others specific to digital media) still apply - a keen-eyed forensic examiner checking for tell-tale signs that the image has been manipulated (shadows are wrong, traces of extra bits from the merged photo etc).
Digital media is just as reliable as evidence as film - that is: "not very, use with caution and bear in mind it can be faked."
Digital signing would be harder to get around than merely faking a negative.