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How to apply mosaic to a photo in such a way that there is 
no way of decoding the mosaic to get back the information?

I need to apply mosaic to the address of a photo that will be
published. Yes , no one is interested in my address but I
just need to just make sure 100%

Decoding by the NSA or by &ramdom_person? If you can't read it it is good enough for most purposes. Personally I don't use the mosaic,
I use Filters>Noise>Spread which is more "random" that the mosaic:

[attachment=755]

If you use the mosaic, it just a matter of degree. Obviously if you replace your address by a single pixel, no one can decode it. And even at under 5 pixels/character, it should be nearly impossible to decode.

You can also consider taking a picture of another house. I once participated in a contest where people would submit pictures and the crowd would guess where they were taken. With a little habit, you gather the various cues and then do some search on GoogleEarth/StreetView.