Leonardo DiCaprio -- My Autographed Mandela Pic was Stolen ... I Want it Back NOW

Leonardo DiCaprio says he's the victim of a heist involving the likes of Nelson Mandela ... and he's out for blood.

Leo took a pic with Mandela when the actor was shooting "Blood Diamond" in South Africa. Mandela autographed the pic for Leo with the inscription, "To Leo DiCaprio, Best Wishes, Mandela, 4-8-07."

Somehow the autographed pic never got to Leo. Sources connected with the actor tell TMZ ... he believes it was stolen.

The prized photo eventually made its way to a company called Moments in Time, which is now selling it with an asking price of $25,000.

Leo wants the photo back and according to the NY Post he sicked his lawyer on the company. But Moments in Time is telling Leo to pound sand, claiming they rightly own the photo.

In case you care, there's this thing in the law called "bona fide purchaser," meaning if someone buys property not knowing it was ill-gotten, they're generally the rightful owner nonetheless.