Mach's picture of a bullet 

The article now says The first to discover this shock was Ernst Mach in his original picture showing a bullet in  a supersonic flow that cause the oblique shock. 

Is this talking about this picture?

I think this is a picture of a bullet fired into stationary air, while the sentence above seems to say that it's being fired into air that was already moving at supersonic speeds.  I suggest discussing this at Talk:shock wave#Mach's picture of a bullet since there is already discussion there, although I suspect a change in wording in this article is required.