If the drive only shows 42MB used, you probably only moved shorcuts of your pictures.
In order for you to copy or move the files properly, you will need to locate the folder on your computer where the pictures are located and select all the photos and copy that to the Passport
Please note that a real backup is having the same information on different locations. (Passport and the Computer on your case)
Please see the following link for additional information on how to copy or move the files.
