The short answer to that question is anyone who is interested in learning more about steganography. But in truth the book is geared more toward the law enforcement and cyber-forensics investigator community. As a forensics investigator, I know that steganography is something other investigators are aware of, but that their knowledge levels can vary dramatically depending on the types of cases they have been exposed to. This book is meant to level the playing field from an "awareness" standpoint. Often, in an investigation it is not necessary to be an expert on one particular topic; what is important is first to be aware of its existence and then to know some of the creative ways it can be used. I do not expect that you will read this book from cover to cover, but you may read a few chapters in a row and use others for reference.
I have structured the book in a way that takes you from knowing nothing to knowing what steganography is and how it fits into the world we live in. The first part of this book covers the basic types of steganography (and there are quite a few), and also some of the events and people that have used steganography throughout history. The second part moves into the specifics of how digital steganography and watermarking work. I took great care in making these sections only as technical as necessary. The goal is to give you a general understanding, not to teach you to write your own steganography algorithm. The third part moves into some of the tools you as an investigator or casual user may encounter on the Internet. This is not a complete list, of course, but it does contain information about a lot of what is out there. The last chapters of the book cover how steganography and watermarking are used in the world and how to detect and defeat them.
I hope you find this book interesting as well as a little entertaining. I hope that it gives you a foundation on which to explore on your own and look in directions you might not have looked otherwise.