I think you are missing the fact that generally speaking, even in courts of today, no single piece of evidence is sufficient for a guilty verdict.
Sure, technically speaking, you can make an image that is awfully difficult to tell that it is fake, and present that as evidence in a case. But if the other side disagrees, they will present their own evidence which contradicts yours.
If both sides present equal amounts of equally valid (in the eyes of the court) evidence, most modern societies fall back to the principle of presumption of innocense. If either side is able to present more or better evidence for their view, then that side usually wins. This is how courts already operate, and while it isn't perfect, it's pretty widely believed to be better than the alternatives.
So if, in your world, perfect faked images and audio clips are commonplace, then the courts would have to operate within the assumption that any presented image, video or audio may have been tampered with or outright faked. As a result, the evidence value of those will be reduced, possibly to the point of being a mere curiosity rather than considered valid evidence.
Suppose that in such a legal environment, I claim that you robbed me in the street, and I am able to present a photograph allegedly showing the event. The picture is good enough that everyone can readily see that you are holding a gun to my head while I drop my wallet on the ground, there are no signs that the image has been tampered with, and all of the image metadata corroborates my story. How might you defend against this accusation?
You might defend against my accusations by providing alternative evidence showing that you were somewhere else. Phone metadata exists in today's world, and very few people in the Western world do not regularly carry a cell phone with them. If you are able to show that the cell phone company had your phone moving through a different part of town at the time of the alleged crime, that:
- shows that you might not have been where I claim you were at the time (at least, it shows that your phone wasn't at the location where I claim you were)
- brings in a third party, which presumably has no particular interest in the outcome of the trial, and thus can be assumed to be reasonably impartial -- this is already the defining principle of witness testimony
Note that cell phone metadata is only one example; there are many others. Another example would be that a bank might be able to confirm that you made a purchase five minutes earlier on the other side of town -- sufficiently far away in terms of distance, and close enough in time, that you couldn't possibly have been where I claim you were at the time when I claim you were there. There is also the seemingly growing abundance of monitoring cameras throughout our society, which could also provide corroborating evidence from third parties. And of course, human witnesses (hey, I was walking my dog and stopped to chat with the neighbor around the alleged time; ask the neighbor, and check their phone location records to see if they agree with those for my phone!) If you are able to present multiple such pieces of evidence that support your story of you being innocent, and I am unable to properly address that discrepancy, at the very least that seems likely to lead to a not guilty verdict, and may also get myself into trouble as having given false testimony.
In the end, evidence which can easily be faked is trusted far less by courts than evidence which is non-trivial or very difficult to fake. Assuming that the justice system remains similar to ours, this would seem likely to not change in your world compared to ours; only the relative trustworthiness of different classes of evidence would change.
It also seems likely that, in a world where much evidence can be easily faked, the penalty for false testimony would be much harsher than it might be today.
Of course, a not guilty verdict does not necessarily imply innocense, but again, that's a trade-off where a society has to choose which alternative is worse. It's either living with the risk of people who committed crimes being pronounced not guilty and walking away, or living with the risk of people who did nothing wrong being pronounced guilty and being sentenced for a crime that they did not commit.