When they cease to be recognisable as a pattern in front of a judge.
> Would a reflection in a window or puddle be in violation?
Yes, as long as reasonably recognisable and substantive of the display. Not really any different the mirror in SLR camera taking the picture.
> What about an aerial shot of Paris?
Probably not, as you wouldn't be able to see a distinguishable amount of the lights from an aerial shot. Depends on the resolution.
I'm not sure what you think your opinion adds then tbh.
> IMHO, if you want your copyright to be upheld, the creator needs to show a reasonable amount of effort to limit possible copyright infringement.
For the avoidance of doubt this is not legally true in almost any circumstance in pretty much any country in the world.
Pedantic point but the mirror isn't involved when a picture it taken. It flips up out of the way and the light goes directly from the lenses to the sensor/film. The mirror is only there for the viewfinder.