Ahh, I misunderstood.
That's not good; it sounds like he may have told Ghost to do a drive-to-drive (or partition-to-partition) image, instead of creating an image file in the existing file system on the USB drive. If this is the case, then his original data is probably not recoverable by mere mortals.
TestDisk is a reasonable thing to try, but I would not be optimistic.
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