I recently put the SD card of my camera in a Windows 7 PC and start browsing pictures on it. I noticed some were not aligned correctly and use rotate feature included in Windows Photo Viewer in order to view them as I wanted.

What I didn't know is that when rotate feature is used, it also overwrite the picture when pressing next or previous button resulting in a possible loss of quality (which is in my opinion a bad idea, app should at least warn user of what will happened when using such a feature).

After that, I re-inserted the SD card back in my camera and bad surprise happened : the rotated picture could not be previewed anymore. Instead, i got a black screen saying "Incompatible JPEG format". Other files (untouched) are still working ok.

To try to understand what happened I opened a JPEG file from camera and one generated on windows 7 in a hex editor. Here is the difference :

The camera JPEG files have a Exif tag in them (with 0xE1 in header). Other JPEG files (Windows 7) have first a JFIF tag in it, followed by a Exif tag (with 0xE0 in header).

So if i understand it well, both are JPEG files, but using a different internal format.

Here is my question : is it possible (using some tool) to convert JFIF files to Exif format ?

I understand that original camera files have been reencoded and thus lose some quality (getting originals back is impossible). What i want know if convert them from JFIF back to Exif (without a second loss of quality if possible...)