The photo is interesting because it shows the front of Dumervil's shirt untucked and hanging over his shorts ... relevant because the alleged victim had told police Elvis and another man both approached her car and lifted their shirts to show they had guns tucked into their waistbands.

According to the police report, Dumervil had been driving a Land Rover on Saturday ... and following his friend who was driving a Mercedes ... when a woman in an Impala merged between the two cars ... upsetting both Dumervil and his friend.

The men allegedly got out of their cars ... approached the Impala and threatened the female driver while flashing their guns.

Dumervil -- a two-time Pro Bowl linebacker -- told police he didn't have a firearm ... but cops say they recovered a weapon in the glove compartment of the Land Rover.