This is usually due to the modification of the image.  It is possible that the image may have been resized, edited, sent in an email, or it is a copy of the original image.  

Any of these things will change the electronic date, which is what WISE reads and uses.  

To make sure this doesn't happen, we recommend importing directly from the SD card.  

Importing directly from the SD card isn't a must, but it usually prevents any issues.