For my browser (Google Chrome), the 12 appears larger when going back and forth between the two images, even though it's only shown at 86% while the 8 is at 100% in the photo viewer. If you click on each one again to open it in a new web page then you can clearly see the difference. I'm guessing the browser has a maximum size it will show for thumbnails since the 12 looks about as big as I can remember seeing. If the image is smaller it shows it as is, if the image is bigger it scales it back down to whatever the max size is and shows the percentage it scaled to when you hold the mouse over the picture. Looks like the max is somewhere between 8in and 12in using your software to size and my browser to view but I imagine it could be different for other software and browser combinations.