I am wondering if the intent was actually not to be racist, but to make fun of PD.
I guess I would have to see the actual picture for context. If it's a serious picture, I would think it was probably racist, but if PD had a goofy look on her face or something like that, I would think that the intent was to mock PD, which, if that were the case, might be seen as a statement against racism. Not the way I personally would choose to take a stand against racism. But maybe it was a well-intentioned attempt that just missed the mark.
I don't know if that would make the picture okay, though, especially not at work. It's just too touchy of an issue and could be taken multiple ways. I think if I were you, and it comes up again, I would refer to it as "the picture making fun of PD" and see how that flies. If there is agreement, you are cool. If you get shocked looks or outright denial that this is what it was, then you know what those people are really like.
In any case, I would just pretend like it didn't happen, just be civil and professional at work, unless something else happens.