The printer is "small" enough to fit inside of two suitcases, thereby making it a "portable" printer. The device can only print one color at a time (it requires a human to change the spray can), but otherwise will drag around the can of paint using two pulleys under computer control.
The creators have won an award at the 2003 Machinista Art Festival, which has an oddly horizontal design.
If you want to see pictures, go to the home page for Hektor (the name of the "printer") and click on the JPEG icon. You'll get a half-dozen or so new windows.