I'm not familiar with G4L, but it would probably help to know how the image was created. I've used dd, fsarchiver, and partimage to image my systems in the past. They work differently, and an image created by one of them must be restored using the same tool. Your best bet is to ask the person who provided you with the image. If that doesn't work, here are a couple of specific questions for you:
1. Is the image bootable - in other words, can you boot the from the USB drive?
2. If the image is not bootable, then boot your computer, and plug in the USB drive. Can you see any files on the USB drive, and if so, what are their names?