Probably outside of the scope of what imagemagick can do but maybe I am surprised. I wonder if its possible to either sign or embed information in an image by altering the pixels into what it can work similar to a QR code.
The idea is that the image would have some minuscule pixels alterated withing the picture, and a scan could be able to detect the values of the pixels and extract a messag or signature. While plain look wont be able to detect such change.
If anyone have ever heard of this or done something, would be helpful.