Sources tell TMZ ... Kim Kardashian and her sisters, Khloe and Kourtney, were shooting their reality show this week in The Oaks ... the double-gated Calabasas community where Kourtney lives. They noticed a Dodge sedan parked near the shoot which lasted nearly 8 hours.

We're told at the end of the shoot, the Kardashian trio walked past the Dodge, when the person inside poked a camera out the window and started shooting. The girls confronted the dude, saying he was shooting in a private, gated community, and the guy began profusely apologizing.

We're told Kourtney called the cops and The Oaks community security who came a-callin', and quickly determined the photog had a pass to get into the community by another resident -- Keyshawn Johnson.

Our sources say security told Kourtney that Keyshawn would be fined $1,000 for letting the guy in.

We spoke to Keyshawn who says he did approve a pass for the guy -- but only to make a delivery to his home. He also says he hasn't heard anything about a fine ... which, by the way, would have to be voted on by the homeowner's association.