Behind the scenes of The Blackguard (1925, dir. Graham Cutts). Art direction by Alfred Hitchcock... Hitchcock either engaged [German director F.W.] Murnau in conversation, or overheard him tell others: “What you see on the set does not matter. All that matters is what you see on the screen.”Via Old Hollywood.
Hitchcock never missed an opportunity to quote this remark, which became a cornerstone of his own approach: The reality didn’t matter if the illusion was effective. He then emulated Murnau by hiring a slew of dwarves to stand far from the camera in The Blackguard, creating an artificial perspective for a crowd scene.
-excerpted from Patrick McGilligan’s Alfred Hitchcock: A Life in Darkness and Light
And speaking of "forced perspective," when I double-checked the term, I encountered this example:
The Potemkin Stairs in Odessa extend for 142 meters, but give the illusion of greater depth since the stairs are wider at the bottom than at the top.