Seebeck reprints
The name of Seebeck is something that many stamp collectors and philatelist recognize at some level. He was a stamp dealer and printer, best known for his stamp-printing contracts with several Latin American countries in the late 19th century producing loads of stamps to collector markets.
Last month I started organizing some of my mint / unused South American duplicates for exchange, and I was not surprised that I ended up with something I believe to be Seebeck reprints. As I have for some time build a “side collection” on “Errors, Freaks and oddities on worldwide stamps” (where I accept both mint and used material) these immediately caught my interest (of not giving them away).

1896 Nicaragua - Official stamps. I believe these are Seebeck reprints.

1896 Nicaragua - Official stamps. A larger view for some of the stamps. Notice the differences in print colors and accuracy (especially 1c value compared to others).
For what I’ve read, the hard part with Seebeck reprints is that there is no easy way to tell apart if the stamps are from the original printing or reprints. Seebeck’s agreement allowed him to use use the original plates for unlimited reprints. For some issues the difference between original and reprint can be told by paper or stamp color, but it’s not a very reliable rule as Seebeck was not very consistent with quality even with the original issues. I asked advice on several forums, and the best answer I got was what I already know – “if it’s unused, then assume a Seebeck reprint”.

1897 Nicaragua - Official stamps. Reprints as well I suppose.

1897 Nicaragua - Official stamps. A larger view for some of the stamps.
According to Michel, the reprints should have thicker paper and a bit brownish color instead of “brick red”. My problem was of course “compared to what” as I don’t have the originals. After some googling I managed to find a sample of collection from David Feldman auctions (Warning: a very large pdf-file) that helped me in determining some details about the original print colors.

1898 Nicaragua - Official stamps. More Seebeck reprints I believe.

1898 Nicaragua - Official stamps. A larger view for some of the stamps. Once again, there is a very clear difference in color shade.
You might also be interested of related posts about Forgeries, Stamps and postal history of Nicaragua.

I both hate and love these stamps after distinguish the original from reprints is both difficult and a real challenge, I think a good starting is paper and postmarks, I don’t think color will help specially considering red color is easily affected by sunlight.. what about the uv lamp… maybe some differences are seen…
@Nicolas… AFAIK (identifiable) postmarks are the only reliable way to identify the reprints from real ones. For what I’ve read, it’s another jungle (forgeries etc. fun stuff).
Otherwise these are to best of my knowledge pretty impossible to categorize properly.