Well, if your photos are set to backup to iCloud, then when the next backup occurs the new photos will be backed up because they are now in the Camera Roll.
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I would just merge all your images into one folder on your computer then copy them back over to the DCIM folder (overwriting the duplicates).
I believe too, what you want is this:
/var/mobile/Media/PhotoData
The path you mention I don't have. iOS 7.1.2.