Overprints and surcharges, which are a subset of overprints are one of the most problematic areas within philately for two reasons:
- Many of the world's rarest stamps are common stamps that have been overprinted.
- Many overprints have been extensively forged, due to the difference in value between unoverprinted stamps and overprinted stamps.
The quality of the forgery work on overprints varies from extremely poor overprints that look nothing like the originals, to extremely good forgeries being made with laser printers and other specialized equipment. Consequently, certificates are a must for a lot of more expensive overprints.
But what about less expensive stamps that are not worth the cost of a certificate? Fortunately there are ways that you can learn to spot forged overprints. The best way to explain how to spot the differences is to go through an example. Look at the two Canada #O9 50c Lumbering stamps with the scarce O.H.M.S. overprint shown below: