So back in at least the 1st and 2nd video game generations (pong clones, Atari 2600, Fairchild, Odyssey, etc.), all game graphics, sound effects and music were created programmatically in code. If you wanted a little person to be the main character, you had to plot out and draw the pixels for them. Music was done by manually sending signals to the sound chip, or something similar.
But when did this change? I figure with music it is pretty simple: CDs being used as the storage media brought real music being worked on externally that was then simply packed-in with the game. But what about the graphics? At what point in game history did developers stop writing code to create their graphic assets, and start actually drawing them in paint-like programs and import them into the game?
Specifically, were art assets for the NES (Famicom) created in code, or imported somehow from art programs? The NES is the one I can't really pin-point, since it seems like everything before was created programmatically, and everything in the generations to follow have clear signs that the graphics were imported (such as digitized images in games like Mortal Kombat or NBA Jam on the SNES).