My thoughts about duplicate content/articles.

Hey guys. First off, let you to know english isn´t my primary language, so I´ll try to make this the more legible possible, and please excuse me if I don´t fully achieve it.
I´ve been reading a lot about duplicate articles and how to avoid it. I looked at every spinner and rewriters you can find in the net and read a lot of "theories" about how search engines detect them and qualify them for duplicate or not.
And, my conclussion is...nobody actually certainly know how the search engine´s algorythm works, which is vital for us. We need to "think" like the engines do if we want to give them what they like. Everybody has his own idea about this, some people will say that replacing words in a medium to high percentage will get the job done. That´s why a bunch of spinners doin this exist in the market.
But, while searching this issue, I came across with something on a site I don´t remember, that I think it´s the best approach on how Google and others dup detection softwares think. If this is true (I´m pretty sure it is),
99% of spinners out there are useless:
I´ll graphic this idea with a real life example:

You have a good friend. Obviously you know him and you are able to recognize him instantly if you see him walking down the street at a medium to close distance, right?
Now, did you think that this happens in any circumstances? I mean, notice that no matter what colors or clothes he is wearing, if it´s winter and he´s wearing a thick jacket or it´s summer and you find him in swimswit, if he´s wearing sunglasses or a hat, or whatever he is wearing. If thinking on a woman, you will also recognize her if she is wearing some heavy make up or with a new hair style!.

This is what happens with search engines. You can change all the words you want, (different color shirts or different makeup) but they will still recognize the content because they see (like we do with our friend) the WHOLE PICTURE. They look at the entire context of an article and find the "footprints" you left, they are, not the words you changed but the ones you DIDN´T change. Your friend´s face and body type are always the same, no matter what they wear or the makeup they use. Unless they go thru a heavy esthetical surgery or lose or gain 100 pound of weight, you will keep recognizing them easily.
Look. If you spin an article, you can then erase the spun words from the original and their synonyms from the spun version, so only the non touched words remain in both versions. Those are your footprints, along with the number of paragraps and word count. If You have those same footprint words in the same order than the original in your spun version, search engines wil rapidly recognize them. You can´t obtain this type of similarity unless the two articles are using the exact same "seed".

Just my though. Anybody agrees with me?