I'm a mac user with seagate external HD. I've recently thinned out my photo files on my mac and want to back up the computer to the HD. My previous back up included many photos that I no longer want but they are on the external HD from the previous back up. Will those photos remain on the HD even though my next back up of the mac doesn't include them since I deleted them? Basic question is when I back up, it does not toss the photos from the external HD that are not now on the computer. Hard to explain, hope someone understands. Thanks.