Eva Green's semi-nude photo for a poster promoting Sin City: A Dame to Kill For ignited a mini-scandal when the MPAA refused to allow the poster to be displayed in movie theater lobbies.
Fortunately, rather than throwing up their hands and resigning the posters to some exec's "private collection," the studio slightly altered the shot to gain the powerful association's approval.
Check out the ever-so-subtly-changed before and after posters below and see if you can even distinguish between the two.
Yes, the gun in Eva's hand isn't the part that concerned the MPAA, rather it was the "curve of under breast and dark nipple/areola circle visible through sheer gown" that had censors concerned the poster would warp impressionable young minds.
So the studio simply sent the poster back to the lab to have Eva's robe made slightly more opaque and voila - acceptable boobage.
To answer your question: yes, the MPAA really is that powerful and that fickle. In the past the shadowy organization has doomed films financially by slapping them with X or NC-17 without even offering an explanation.
So yeah, if those folks tell you to cover some boobs, you cover some boobs.
Check out some other memorable movie posters in the gallery below. Hopefully, none of them will offend you.