The term cover pertains to the outside of an envelope or package with an address, typically with postage stamps that have been cancelled and is a term generally used among stamp and postal history collectors.
I have had this scanner for almost 4 years and scanned everything from brochures, photos, receipts and multiple sizes of papers. It scans at 30 pages per minute and can do the front and back at the same time. The scanning speed is very fast but it is quiet too. It is easy to clean the scanning mechanism after scanning a dusty scrapbook or old photo. Making the next scan as good as the first!
If you are looking for an all in one negative/slide/photo scanner look no further. This thing is great. There is a brief learning curve and you need to experiment with all the settings and how to use the included holders. Also, when working with negatives and slides dust is not your friend. Compressed air and a soft brush are helpful. We have been using the Espon V550 everyday for over a year and have had zero issues.