I've seen this same effect......I think it may have to do with any of several issues, but I've mainly narrowed mine down to the camera's handling of .jpg's, or the transfer method to the computer. When I plug my camera into the front of the computer itself (a USB 2.0 port) it will work fine. If I use one of the ports to go to a multiport USB extended (especially those that derive power from the computer), I can see corruption as I upload the pics from the camera to the computer.
So, I chalk it up to one or both of 2 things:
1. A difference in the .jpg software in my Panasonic FX12, as it compresses and the Windows viewer that uncompresses it. I have not tried specific pics in different viewers, as frankly, that thought never occurred to me. I just assumed they were corrupt and lost. Most were not critical, so I just deleted them.
2. The USB hub I used was defective or has issues getting all data transferred (there is probably little if any error recovery when uploading) to my computer. Once the picture is on the system(and has been viewed and verified intact), I've not had them go bad on me.
I would suggest you pull the card and use a card reader as someone earlier did when you upload (if possible) or be sure to connect to at least a USB 2.0 port directly (no hubs involved) into the system you are uploading to. I would upload (temporarily) to your internal harddrive. Then, I would load & view ALL of them to be sure they are good in your viewer. After that I would move them to your external drive (via copy), and verify again. If all goes well then, I would back up to a CD/DVD and verify once more.
That is overkill if they are not very important photos (not all I take are even worth keeping! LOL), but you could surely narrow down the possibilities.
I would also verify they are good in the camera before any of this. I did find 2 pics that were corrupted in the camera itself, so that's why I believe the compression/decompression is buggy in the camera. But that's just my take on it.

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