At Seattle airport we weren't aware of any such technology or specific opportunity to do a "capture". Yes, they do use it overtly in certain locations including the security check point, but it was just not in use today.
However, at LAX we did encounter it even though we were already at the gate and already within the secure area. Strangely the LA Police had setup a screening point just before our gate with facial recognition cameras. It seemed odd, because they didn't ask for any ID, they just wanted all the passengers to step up to the cameras one-by-one to have their image captured. Once the camera snapped, it flashed a green light and they let us proceed to the gate. We can only speculate why the local police were using this tech at the airport, but it seems rather odd and seemed like this was a semi-permanent set-up they use frequently.
The Virgin Atlantic plane was a Airbus A350-1000 that seats between 350 and 410 and our flight had a crew of 13 and only 38 passengers! The passengers were very spread-out and only a few individuals for each cabin. We're really lucky they didn't cancel the flight as that same flight was cancelled today. Heathrow airport was a breeze and almost empty. We waltzed through immigration and customs with no waiting, no lines and completely contact-free! The only thing we waited for was baggage claim.
From the airport we took a charter bus to the train station. The full size luxury bus had only 2 other passengers besides us. We got to the train station a bit early and were able to get a train ahead of our original schedule. A few stops had quite a few high-school students, but for the most part the train was also mostly empty and everyone was wearing masks. After the train we found a taxi for our last mile to the VRBO house, which was a great blessing because each of us were pushing about 90 lbs of luggage all together. Now we begin our 14 day self-isolation period. More from Becky tomorrow.