Scanning previously printed work is not recommended unless:
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(a) you are the legal copyright holder,
(b) the dot pattern used for printing is extremely small and of good quality,
(c) the new scan will be reduced smaller than the original.
Printed work such as advertisements or even photocopies are not suitable for scanning and enlargement. During the printing process, colors are reproduced by means of a smaller palette of small dots. These become more evident when scanned (sometimes resulting in undesirable patterns called moiré), especially when enlarged.