I have a basic Cannon Powershot point-and-click camera and have had a strange issue when transferring photos to my computer. I am using the software that came with the camera, Camera Window. I recently transferred some duplicate photos and noticed that they have different sizes and previews from the same ones I already transferred. The Finder shows different file sizes while Preview shows them being the same. Could the originals have an embedded preview that is causing the larger file sizes? Any other explanations? I'm going to get a card reader later, I'm just wondering which copy of the photos to keep.