James Franco -- Photog Files Police Report ... For Takedown at Concert

James Franco took down a photog while leaving the Lana Del Rey concert Friday night in Hollywood ... this according to the paparazzo -- who now wants justice.

Franco attended the LDR show at the Hollywood Forever Cemetery and based on the pics it looks like James may have just been joking around when it happened.

The photog obviously wasn't playing around though ... he went into an LAPD office Saturday morning to file a report -- claiming he's got broken equipment and a minor back injury.

We're told police will pass the case onto detectives this week.