People watching The Ten Commandments in a drive-in theater in Utah, 1958.

this one is via redditt
"from my mom...I had forgotten about some of these details so thanks for asking. He sat with Cecil B. deMille to choose the best single frame of Charleston Heston to be used to create a film loop that could be projected for a time exposure. Then he had to find a drive in with a scenic background which was not easy, most are in the bad parts of cities. He found the drive-in just outside Salt Lake City. DeMille wanted to be sure the film had run in the theater. Turns out the movie had been shown to more people in that drive in than any other place in the world because the Mormon Church made it a requirement.
He had a large pane of clear glass mounted in a frame and positioned it to fit the image size on the screen to create a mask. He covered it in black and set his camera on a tripod. Color film at that time had an ASA of 6. He developed a unique technique to shooting images off of screens which required an additional low level light to affect the film if it was shot in a dark theater, but because of the first exposure already present on the film when he shot the loop, he didn't need it for this.
He invited college students up from Brigham Young University by offering them a free movie if they arrived before dusk. They came and parked their cars, and he shot the first frames as the sun set. He had arranged for the drive in to run "And God Created Woman" with Brigitte Bardot for them. That was a real hit. Once everyone left, in the dark of night, he ran the loop of Heston. That's how they did it prior to PhotoShop. Two shots, one piece of film two different exposures. Very technical to bring it off. Your uncle, age 14, is sitting in the Corvette convertible which he got to drive himself on the salt flats which was pretty cool, getting to drive a fast car and a first adult movie all in one adventure.
His work took lot of imagination, lots of technical planning, a lot of charm and an ever present sense of the ironic. Glad they enjoy it and included the credit."