I have used clonezilla http://clonezilla.org
along with parted magic http://partedmagic.com
to achieve something similar. Parted Magic is a linux live cd that is small and boots directly into ram. It has a program called gparted on it t hat can be used to resize, create, and delete partitions. I use this to shrink down the ntfs windows partition and create about a 20 gig or so ext3 linux partition.
I then use clonezilla to create an image file of the windows partition and save it on the ext3 partition once I get everything set up the way it should be in windows. Windows doesn't even acknowledge there is a 2nd partition in my computer. You can use the clonezilla cd to reimage the windows partition from the image file on the ext3 partition. Clonezilla will only copy the data to the image file and compress it.
You can also save and deploy images from an external hard drive, or even a network share using clonezilla (use the samba server option to connect to a windows file share).
If your machines can boot from a usb drive, you can use 2 usb thumb drives, one for clonezilla and the other for parted magic. The easiest tool to do this I have found is called Unetbootin http://unetbootin.sourceforge.net/
Unetbootin can put about any linux live cd on a usb thumb drive and make it bootable. I hope this helps.
I also am currently playing around with a fog server at work. So far it seems pretty neat. It uses PXE booting to be able to remotely deploy images to computers. You can also create "snapins" which can be used by the fog server to install software on the windows clients. It also has an inventory tool with it. It gathers the hardware info of a computer and stores it in its mysql database. The hardware info can be exported to a csv file at any time using the web interface of the fog server. You mentioned about traffic across the wan, depending on site size, it may be useful to set up a fog server at each site. Then your images would be hosted on the LAN for each site, The only WAN traffic would be when interacting with the web gui on the fog server or copying an image file between sites to the fog server for deployment over the LAN.
Good luck !