Hi Joe,
This is the Assignment interface, not the Gradebook one.
I do not know about thumbnnails, but you can try out this patch MDL-7206 which allows to zip/download all submissions at once,
We put 1.9 ones on our testing environment to look at, and even though there can be some glitches, it seems to works pretty well
Gradebook
Viewing thumbnails of single image uploads
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