I have many pictures on my PC ( about 20,000 jpg files ) that I have backed up to an external hard disk and also burned on DVD.
I used beyond compare tool to compare the pictures that on my PC with the pictures that on the external drive and the DVD - all was identical.
Few days ago I have compered it again and saw that the files size is not the same
meaning both "size" and "size on disk" properties of the files on my PC is less ( in several KB ) then the files on hard disk and DVD.
I use several SW like Picasa and Photoshop but only to view the pictures not edit them so I don't know what cause this change.