An A320 flight crew was accused by a licensed pilot passenger of taking off with contaminated wings which he had documented with photos taken during the takeoff.

Narrative

We arrived at the aircraft in the early morning; noticing light frost on wings and tail. I immediately walked through the cabin and examined wing surface. The First Officer was doing aircraft acceptance. We agreed to reposition aircraft into sun at scheduled departure time due to no deicing equipment on field. Due to expected extended taxi we added 1;000 LBS of fuel. Due to unexpected boarding issues and fueling delays; we pushed back 1:40 late; negating the need to park in the sun. By this time frost on wings had become a non issue; because the sun had been up for 30 minutes. During the push we observed other aircraft that were parked next to the terminal facing the same direction and their tails and wings looked good. We performed yet another contamination check and were in agreement that the aircraft looked safe. We slowly taxied out giving plenty of time for engine warm-up; performed yet another contamination check utilizing all company detection procedures. After several inspections of the wings; three from the jet way looking down on top of the wing and at tail surfaces; and one from the cabin we safely took off 42 minutes after sunrise with what appeared to be a clean aircraft. In summary; the First Officer and I were in total agreement that the aircraft was safe; and neither cabin crew nor passengers expressed any concerns. After takeoff; the flight was uneventful. Upon arrival we were notified by ACARS to contact Scheduling. They informed us we were to deadhead to ZZZ on the next flight. After departing the aircraft we received a voicemail to contact the ZZZ Chief Pilot who then ordered us to return to ZZZ and come to his office directly. We asked why and he stated that a passenger; who is also a corporate pilot; submitted incriminating photographs that we flew an aircraft with possible contaminated wings on our just completed flight. Why didn't this pilot ring the call button to notify the crew of his concerns? This professional pilot instead allowed the flight to continue despite his concerns. He then used his electronic device to photograph the take off. We have been informed by the Chief Pilot these photos show evidence of moisture flying off of the top of the wing surfaces. We have not been allowed to view these photos. With the current facts we still believe we followed all company procedures and we departed with an aircraft that was free of any contamination.