Remarqued Stamps - What Are They?

Hi, this may not be the forum to ask this question but I would like a primer on remarqued stamps, what are they, how do they come about, how rare, etc. If there is a book, pamphlet, internet link, I'll take that to get me started. Thanks!

First ever time I have come across this term.

The remarque—a very small, original piece of artwork signed by the artist—is a phenomenon associated almost exclusively with the Federal Duck Stamp Contest. The artwork appears in a stamp's margin and always complements the image on the stamp.

https://postalmuseum.si.edu/exhibit...the%20stamp.

As far as I know the concept, a remarque is something original added to a reproduction by the original artist. In my twenties, I collected some prints, and some of them have remarques added by the artist. Some people consider a new signature a remarque, but usually it involves a little sketch. When I've seen them, the remarque has been related in some fashion to the topic of the original work. Value would seem to be in the eye of the beholder.