after several logical reasoning, my answer is "three units".

after several logical reasoning, my answer is "three units".

The possibile right answers to which I have come are the following:

- all units (9).

- for the solutions from 8 to 5 I've not found any logical criteria (unless you believe that the total number of units on the picture is 8 or 7, in this case the "8" and the "7" answer has the same logical criterion of "9" answer)

- four units

- three units

- two units

- one unit

or

- zero units

it all depends on logical criteria that you adopted to determine which units on picture are decoy and what are real.

It depends on which aspects of the game you have considered and which ones you've omitted.

I have a logical explanation for each one of the above answers (if you want I can argue every one of my answers).

I can not say precisely whitch of these solution is the correct one, because it depends on your logical reasoning (which is your subjective point of view ... and not an absolute truth on which everyone can agree on).

Clearly there are two Decoy units in this picture:

1.  Far right. Only a Decoy would run into battle holding a vacuum cleaner. That is not a weapon from this game, or a recipe for success in warfare. Although he could clean the place up in a jiffy.

2.  Second in from right. While Al Jolson-styled minstrel face paint is a great idea if you are attacking a cabaret in the 1920's, doing that attack without the benefit of a left arm (like our Decoy hero here) makes a troop without value on the Zandian fields of honor. Fake. 

Or...

I think answer is 2. Soldier on right dont cast any shadow so he maybe fake and Thunderhead on right dont have radar like they usually do.

1) Helicopter on the LEFT don't have radar (not the one placed on the right!)... however, it may still be an optical effect caused by the distance, by the smoke and by the rapid rotation of the blades).

2) as said by Marek84, the "Vector" units could be a fake, because it has not the shadow (as I also noticed) ...

Furthermore the tube of his weapon is not positioned exactly: if we consider that he holds the weapon in his right hand, the tube should be inside (facing the body of the soldier).

Finally, his helmet is different from what he usually wears.

3) the sapper (placed between the "sniper scout" and "recon operator"), he wearing a different helmet from what I usually wear ... but this does not necessarily make him a fake.

4) inside the building that is exploding (on the left of the image) you can see a figure standing (very small).

This could be a dummy, because no real person would remain in a building that is about to explode ...

However, it could be a victim,

so... a real person who is dying.

5) the same way, always in the same building, you can see a second figure, crouching, inside of a door.

However, this figure is very blurry and maybe it could have nothing to do with the game (this is why I said that the total units may be 8 or 9).

6) Another possible answer is that the decoy units are zero, because the game provides that this special tool "it DUPLICATES troops in enemy recon reports" !!

Therefore, if we adhere to this basic concept, for every real troop shown, there should be a decoy "twin troop".

Since the soldiers shown in the foreground are all different (from left to right: scout sniper, sapper, recon operators, commando, Vector) we should have for each of them a fake copy.

Since in the picture there is not a decoy unit for each of the men shown in the foreground, this fact invalidates the whole concept that is the basis of how the "special tool" works.

"Decoy Army" tool is not active on this picture, therefore, no units are false (they are all real units).

1) Helicopter on the LEFT don't have radar (not the one placed on the right!)... however, it may still be an optical effect caused by the distance, by the smoke and by the rapid rotation of the blades).

2) as said by Marek84, the "Vector" units could be a fake, because it has not the shadow (as I also noticed) ...

Furthermore the tube of his weapon is not positioned exactly: if we consider that he holds the weapon in his right hand, the tube should be inside (facing the body of the soldier).

Finally, his helmet is different from what he usually wears.

3) the sapper (placed between the "sniper scout" and "recon operator"), he wearing a different helmet from what I usually wear ... but this does not necessarily make him a fake.

4) inside the building that is exploding (on the left of the image) you can see a figure standing (very small).

This could be a dummy, because no real person would remain in a building that is about to explode ...

However, it could be a victim,

so... a real person who is dying.

5) the same way, always in the same building, you can see a second figure, crouching, inside of a door.

However, this figure is very blurry and maybe it could have nothing to do with the game (this is why I said that the total units may be 8 or 9).

6) Another possible answer is that the decoy units are zero, because the game provides that this special tool "it DUPLICATES troops in enemy recon reports" !!

Therefore, if we adhere to this basic concept, for every real troop shown, there should be a decoy "twin troop".

Since the soldiers shown in the foreground are all different (from left to right: scout sniper, sapper, recon operators, commando, Vector) we should have for each of them a fake copy.

Since in the picture there is not a decoy unit for each of the men shown in the foreground, this fact invalidates the whole concept that is the basis of how the "special tool" works.

"Decoy Army" tool is not active on this picture, therefore, no units are false (they are all real units).