Thatís the official term that the USPS uses. These are the stamps that the USPS produced that had a hidden image embedded in the stamp design. You had to buy a Stamp Decoder (it looks like a small magnifying glass) from the USPS to see the hidden image.
One of my customers, M.I. from Tennessee, wrote about these stamps. He asked whey the Stamp Decoder was still available from the USPS when it hasnít produced a stamp with a hidden image in nearly 10 years.
First of all, I donít think the Stamp Decoder is still available from the USPS. I checked their website and could not find it. If they still sell it, itís well hidden. Some local post offices may still have it available. And you can buy one from online sites and from some stamp dealers. But to the best of my knowledge, the USPS doesnít sell them anymore.
Scott #3036, the $1 Red Fox stamp, is the first stamp to have a hidden image. There is a picture of a fox on the hind leg. Scott #3862 is the last stamp known to have a hidden image. This is the National WWII Memorial stamp. A US flag is hidden in the stamp design.
The hidden images are a security mechanism. If the image is there, it is genuine. If the image is missing, it must be a fake.
Here are my thoughts.
Why put hidden images on commemorative stamps? If I was in the business of printing stamps as fakes and selling them to the public, which stamp would I choose? Itís going to be the commonly used Forever stamp at that time. This was the Liberty Bell stamp, now itís the Flag and Statue of Liberty issue. If I wanted to defraud the USPS, Iím certainly not going to print a million Cherry Blossom stamps and try to sell them.
The general public uses definitive stamps. They are used on a huge majority of our mail that bears stamps. If a huge batch of letters arrives with Flag stamps on it, itís probably not going to draw the attention of the USPS workers. If a huge batch of letters arrives with Cherry Blossom stamps on it, it looks unusual. Someone in the back room is going to ask if this post office bought a huge quantity of stamps for the XYZ Company that is making this huge mailing.
Definitive stamps are less expensive to fake. The designs are smaller. Unlike commemoratives, they donít have a lot of different colors of ink used. The designs of definitive stamps are generally not as complex as commemorative stamps. If Iím going to fake stamps, itís going to be less costly for me to fake a definitive issue than a larger commemorative issue.
Why did the USPS stop using hidden images? Accorinding to Terry McCaffrey, the hidden image technology was very expensive. I'm not sure the USPS got a lot of benefit out of it.
If you check out the Links section of my website, I have a link to another website devoted to hidden images on US stamps.