Add a watermark to text message in an Arduino
"Robustness", in the context of digital watermarking, specifies the ability to detect the watermark after some signal processing modification (for images, this might be translation, rotation, scaling, compression, etc.) Some digital watermarking techniques are robust against some operations but not against others. The classifications are:


Robust: The watermark should be able to survive against any and all
modification. This is often used in copyright protection, for
example.
Fragile: This kind of watermark is designed to be destroyed by any
modification to the original. This allows any manipulation, even
slight changes, to be detected. Fragile watermarks are generally used
to enable authentication and integrity verification.
Semi-fragile: The watermark should be "robust" against certain,
defined, modifications, but "fragile" against others. In other words,
the watermark should survive intact under the operations you want to
allow, but be destroyed by anything else. Again, these are used to
enable authentication.




For more information, you might find the 2005 paper A Review Study on Digital Watermarking by L. Jian and H. Xiangjian (in the journal Information and Communication Technologies) useful.