I think it may depend on the resolution at which the original was scanned. Given that death certificates likely fit on a standard size page, I'm not having issues with them.

I'm having an issue (it's not the first time I've notice it, so I know it's been going on for some months) with a opened book that was scanned, showing both pages. The zoom extension I downloaded only distorts the image, so I cannot read the text at all. It's not my original image - it was one I borrowed to my tree. I had just received notice of a comment on it, and the unfortunate original poster is now getting frustrated comments about it being illegible. On the other hand, I can no longer determine why I attached it to my tree in the first place.

Still, I don't recall this being a problem with any media before the shared media 'enhancement' mentioned in the thread you sent me to.