Out of curiosity, what does it say that the file type is for the images you are trying to look at?
Sometimes on USBs weird duplicates show up, saying they're .jpg or .png or the like, but aren't. They almost always have a "._" in front of the file name. These won't open. But usually the normal files are also on the USB.
There is also a possibility that instead of copying the files to the USB that it may have made a shortcut.
Do you still have access to the original files?
If you can, take all the files off the the USB you want to keep, dump them in a folder on the desktop, and reformat your USB. This takes it back to factory settings (and deletes the saved data, hence the desktop dump). This should eliminate it being an issue with the USB. Throw all your old files back on it (or throw a few new files on it if you didn't save anything). Check to make sure it's working. Then check on another computer.
If it's all good, try again if you have access to the original files.
See if any of that helps. Let us know!
Good luck!