system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did they resize photos before computers

Before computers, how did they resize photos to be bigger than they originally were? Like taking a small negative from a camera and enlarging it to be almost poster size.

Or taking a drawing and resizing it to fit a book cover or album cover.
gpt
A photo enlarger beamed a high powered light through a negative or slide onto photo paper.  Raising or lowering the enlarger changed to size of the photo protection, just like a shadow is bigger when closer to the light source.