Passive voice

[khibrattorus]

Hello guys,
My English teacher gave us the following example about passive voice:
Who painted this picture ?>>>>Who was this picture painted by ?

 I found "Who was this picture painted by ?" too odd, shouldn't we say "By whom was this picture painted?" or "This picture was painted by whom?"

[tiorthan]

That sentence is fine, as is "By whom was this picture painted".
Your last version "This picture was painted by whom?" on the other hand is something different. It's grammatical, but it's a word order that puts strong emphasis on "by whom". It's a form of the question that you could use, for example, to express incredulity after someone has already told you who painted the picture.