GA pilot reported an NMAC with another aircraft during approach to LNC non-towered airport.

Narrative

During the approach and landing phase of a VFR flight in VMC; I established myself in the downwind to Runway 13. Before entering on the normal 45; I took note of other traffic on the CTAF; confirming their locations with both the onboard TCAS system and ADS-B display. I noticed another Aircraft Y was North of the traffic pattern area and appeared to be maneuvering North and northeast of the airport. Once I was established on the downwind leg; I noted both the ADS-B and TCAS systems indicated the other aircraft was at my 12 to 1 o'clock and flying directly toward me. Once I was able to visually identify the aircraft; I made an immediate descent to avoid a midair collision. Since the ADS-B system identified the tail number; I used the CTAF and addressed the other airplane asking what their intentions were. With no response; I notified other aircraft in the pattern that there was a Aircraft Y maneuvering near the downwind-to-base turn and the base-to-final turn and that it was not communicating. At that point; the other aircraft replied that they were working with TRACON and were doing aerial photography of the nearby warehouse construction areas; adding that they were above where anyone should have to worry about any collisions.After landing; I called the local TRACON facility to tell the Controllers that they had been controlling a photo mission into the pattern at LNC. The purpose was to make sure that the Controllers knew that the airport taxiway closures in the active NOTAM required additional time given full stop landings were required to taxi back to the approach end to exit the runway. The TRACON Supervisor searched for the Aircraft Y and responded that they were not working with them on any current photo mission; but that they had done so in a completely different area earlier. This situation could have resulted in a midair collision because the (presumably) commercial pilot in Aircraft Y; operating a photo mission was distracted and did not realize they were conflicting with landing traffic at the airport. It was even further complicated by the apparently false statement that they were doing all of the work based on TRACON instructions.