The fastest way will be to use multicast imaging software. This will broadcast over the network, but send the data only once and send it to every computer at the same time (instead of sending it to each computer individually, which would be unbearably slow on a 100M network).
This should take about an hour or two in total to broadcast the image to every computer simultaneously. (More if other things are using the network at the same time).
If you're working with Windows and have a Windows Server 2008 or newer box, Windows Deployment Services can do this, and can also PXE-boot the the computers that are to be imaged over the network, I think (It's been a long time since I've done this, so there may be some other requirements, but this is the gist of it).