I assumed that the issue was less the scanning (which can be extremely high precision, and, in any case, the author had to do to get the half-tone image he was

I assumed that the issue was less the scanning (which can be extremely high precision, and, in any case, the author had to do to get the half-tone image he was working with) but the printing. Once the image is resized and printed in the book, the offset between the dpi of the printer and the half-tone dots was going to introduce new artifacts.