Match grain/noise on a photomontage, is there a better method?

[ZeroCool22]

A lot of tutorials show how reduce noise, but what i would like to know is the best way to match a noise/grain when u add an object/person to the photo, to make looks like that object/person was there since always.

The "ADD NOISE" feature not always give good results, because it's a specific type of noise, and photos have so much types of grain/noise, u can find even different size of noise/grain in a same photo, etc..

I upload a video with the method i learned, (this don't have color matching just the grain/noise):

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For me it looks like do the job, but there are also some photos where u don't have a good place to take a sample of the grains/noise from..