And now I'm picturing a giant array of force-fed markers all firing in parallel. Dig up a several hundred old markers and rig all the sears to trip at once. Even better would be to set up a controller that picks which markers to fire per frame, allowing you to include negative/"transparent" areas.
The real trick would be color selection. You'd either need to pre-sort all of the paint, making sure each marker has its colors lined up correctly, or rig up an on-demand color-selecting feed for each individual marker. Alternately, if you have select-fire available, you could easily do single-color drawings.