I have found that, in Win 7 (but not in previous versions of Windows), if you copy a jpg from the Pictures directory to another directory, say Documents, Win 7 no longer shows the date taken but reverts to the date modified. It seems that it can't figure out that the file is photo once it's out of the Pictures directory! For example, here are four jpg files copied from the Pictures directory to a sim card (it works the same with any directory other than the Pictures directory.)