Factual error: When the car pulls away from the front of the "New York World History Museum", you can see palm trees reflected on the car, revealing that "New York" was actually filmed in California.
Visible crew/equipment: Near the beginning when the Phantom is rescuing the little boy from the back of the truck, as he is hanging from the rope bridge, the safety carabiner holding him up is visible several times.
Factual error: Throughout the movie, any cigarettes smoked are filtered. The movie is set in the 30s-40s. The first filtered cigarettes were from a company called Lorilland for their "Kent" brand in 1952.
Visible crew/equipment: After the villain's have been in the cave at the beginning of the movie (one gets killed by a "skeleton") and they run out, the Phantom is chasing them on his horse. He grabs a bad guy by the shirt and throws him into a tree. Watch when the guy hits the tree- it moves, indicating it's made of foam or rubber for the stunt guy to hit safely.