Most photos are printed at 300dpi. This means that for every inch of your photo, there's 300 tiny dots of ink. When we scan at 300dpi, we capture that exact same amount of information. This means you can reprint your scanned image in exactly the same detail as the original.
If you do use this scan to print a photo – or calendar...or wall canvas...or page in a photo book etc. – at a larger scale than the original, it will degrade in quality the more you take it beyond its original proportions.
Scanning at 600dpi takes a lot longer than 300dpi, hence the additional cost. Instead of capturing the digital equivalent of 300 printed dots, it captures twice that. This means, in our example above, the degradation still happens, but you're protected against it a little bit more.
Do you always choose "Speedy boarding", even when you might not use it? Always buy the phone with the biggest memory, knowing you won't get close to filling it? You'll probably like 600dpi.
Here's two scans of the same photo, one at 300dpi, the other at 600dpi. Click the link to open and view the files on your own devices. (Files open in new window and you can save the files using 'right-click/ save-as'. We recommend zooming in on different parts of the image to compare resolution and differing degrees of pixelation.