The 2007 musical Across the Universe which uses Beatles songs to tell its love story about Lucy and Jude, got a PG-13 in the US and marks one of the few films since the 90's to achieve this rating despite showing naked female breasts. Producers normally evade such "dangerous" scenes that can usually send a film into "R"-rated territory quickly.
However, one shot seems to have upset the MPAA board since Evan Rachel Wood's nipple was digitally retouched while other scenes feature Wood's breasts as they are. Both the US and all international versions we know are censored this way. Fortunately, the bonus material section features an extended version of the songs and here the breast shot is intact.
Lucy's nipple was digitally removed in one shot