It just means that the "Creator" and "Type" codes have been changed. Download ResEdit from
www.versiontracker.com, and in it, go to File-->Get File/Folder Info, and the select the file. Change the "type" to "JPEG" and the "Creator" to "ogle."
Do that to all the files and they'll open in Picture Viewer.
I also hear there is way to change them all at once, though I don't know where to get the program.
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Be Happy.