The humanoid in question is the following object:
It's basically a straw man used to scare crow. So I think both straw man and scarecrow are valid names for it. However, the dictionary says straw man also has another meaning:
someone, often an imaginary person, who is used to hide an illegal or secret activity
I think this meaning has nothing to do with scaring crow, but I'm wondering, with the existence of this additional meaning, if these two words are still interchangeable when referring to the humanoid without causing ambiguity.
Best Answer
In US English, the humanoid objects in the picture are only ever called scarecrows. The term straw man is only ever used in a metaphorical sense. If you said, "There was a straw man standing in the cornfield", it would be perfectly understandable, because there is obviously not an imaginary person in the cornfield, but it is not the normal way to say it.