Sure, no problem. You can see this effect more clearly in another version of Alice's Adventures in Wonderland.
In particular, take a look at page 89 of the PDF. As you can see, the bottom portion of the illustration is enhanced while the rest of picture shows a different pixelization.
What's happening here is that the scanning software draws a box around the elements that will be enhanced or not. Since it's not perfect, parts will be left off, and it doesn't matter if it's a picture, text or signature. If the software doesn't recognize an element, it won't get changed. That's why some elements in Obama's certificate look different when blown up.
Again I have to complement you for coming up with examples that might seem to be single scans, but I don't think the stuff from Google qualifies.
I didn't see any pictures on page 89 of the book, but I looked at the image you offered. The lines at the bottom are simply not from a scan. They are all a uniform black (RGB=0,0,0) and are not a product of a scan. Maybe they are some frame that Google added? I don't know. As I said I didn't see the source for this.
And it doesn't matter. I did Google =google books scanning technology= . It's pretty clear that Google has their own proprietary system. This isn't something that would be necessary or available for scanning any document received from Hawaii and in fact nothing similar happened in the other pdf the White House released at the same time.
ML/NJ
