Resolution problems – resampling or adding more pixels
Occasionally, you might have to deal with pictures that don't have enough resolution for the task you have in mind. For example, let's say you are preparing a family photo album but soon discover that some of the older photos that were scanned from the originals are too small; the images can't be enlarged past the size of a matchbox without them appearing soft and fuzzy.
Note
Refer to Chapter 3, The Basics of Image Editing, the Understanding Picture Resolution section, and Chapter 8, Exporting the Finished Work, the Resolution revisited section, for more information.
Much of the free software available for producing digital book products have in-built warning symbols that appear as soon as you over-enlarge an image on a page. These warnings are there mostly to protect the company from complaints that the images being used are low-resolution. You could, of course, still complain, but the proof for the book company...