This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Codebook. picture of codebook for telegraphic correspondence from english Union codebook pic from NSA museum PDUSGovNSA PDUSGov English History June Matt Crypto KB same name Codebooks Books and manuscripts in the National Cryptologic Museum
Page 2023 Free-images.com. All images are Public Domain