A long with everything that's been said
Reflections of a object will tell your brain if it's real or fake.
If the reflection matches the material then your brain will say .real.
If the reflection does not match the material then your brain will say .fake.

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In reality

1.we have natures creations. animals,insects,vegetation,water etc etc
practically imposable to render realistically.

2.we have natures creations forged by humans.glass,metals etc etc
realist renders very.

3.we have man made materials. plastic etc etc
fairly easy to render realistically.

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Some photo's will look fake.why ?

If you take a photo of a plastic sphere.
It's a real life photo of a man made plastic sphere that we can touch.
So is it real ?

How do we know when where looking at a Real photo of a plastic sphere ?
How do we know when where looking at a Render of a plastic sphere ?

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The Artist that will fight for decades to conquer their media.
Even if you never know their name ,your know their Art.
Dark Sphere Mage Vengeance