Hello.
Having stuffed up in the early days of getting access to my daughter's 600dpi scanner. I now always, first off, create an archive copy. These days on to a memory stick.
Then as soon as I go to modify a copy from my archives copy I, SAVE AS, that copy to a new name, that way any save while you are playing around with the image, you still have your original as a back up.
With flat scanners there is no need to put a weighty lid down before copying. I just use a sheet or two of A3 white paper on delicate objects. Or a white towel is good for bound objects etc.
Would NOT recommend attempting a scan through the scanners where the scanned object moves, and not the scanning wand. Had a nasty experience in an archive where the delicate map being scanned appeared to be slightly off alignment, and when the Librarian tried to assist it's passage through the machine, got fouled on the chair they were leaning over, the scanner moved on it's table, and the map then fouled adjacent appliances. giving it a nasty crease.
I spent a combined 12 days researching in that archive, so after a few days the archivist librarians just left me at the end of the day, to photo copy the 20 or 30 pages I had flagged for copying.
After that experience I was extremely pleased I had insisted upon them making, for my research at home, a B&W copy from the map.
- Alan.