What protection does Doom 3 use?

[reddragon105]

the game is on 3 CDs and i thought i'd make a backup of it on DVD for convenience while installing, it seemed simple enough in theory and i've done it with a few games, like KOTOR, XIII, ETM, etc.

so i copied all the files from each cd to a folder on my hard drive. ran the setup from there and it installed fine. burned the folder to a dvd image and tried again. it asked for disk 2.
tried another image, this time naming the disk DOOM3_2 (the name of disk 2). it worked! but of course... asked for disk 3

obviously theres no way i can name the disk both DOOM3_2 and DOOM3_3, is there any way i can trick it?
also - how come it installs from hard drive, with none of the original cds in, and not dvd? as the folder is just called new folder. so it doesnt care what the hard drive folder is called but cares what the dvd is called.
________
starcraft II replay