It's not about OCR or dirt. It's about taking an image. I doubt OCR would work on any of them, whether you use a $$$$$ archivist to photograph the pages or not.
As for below the topmost layer, you're right, an iphone camera won't do it. But worrying about that comes much, much later.
As for below the topmost layer, you're right, an iphone camera won't do it. But worrying about that comes much, much later.