Many people, near and far, have guided this book to completion.

My parents, Jan and Bob, have given me nine full lives or so it seems. My four cats, Plasma Tigerlily Zoya, Sanibel Delphinium Andromeda, Lambda Catculus Puddingcat, and Josephine Antoinette Puddingcat, have provided constant supervision and contributed to testing the cat recognition software in Chapter 3, Training a Smart Alarm to Recognize the Villain and His Cat.

My readers and listeners have taken time to provide valuable feedback and ask questions about my previous books and presentations. Thanks to their loyalty and dedication to discovery, our shared exploration of OpenCV goes on!

My clients at Market Beat, in El Salvador, have inspired several of the book's topics, including detection, recognition, tracking, and the use of Raspberry Pi.

Thanks, Steven Puttemans, for the helpful discussion on Haar features. Thanks, Tanya Suhodolska, for icons used in the application bundles.

My editors at Packt Publishing have once again given me all the benefit of their skill, experience, and professionalism in the planning, polishing, and marketing of this book. Writing one of Packt's "Secret Agent" books has been a uniquely fun project! Thanks, Sam Birch, for suggesting Eulerian video magnification as the topic of Chapter 6, Seeing a Heartbeat with a Motion Amplifying Camera.

My technical reviewers have once again saved me from sundry errors and omissions. Read their biographies here! They are fine members of the OpenCV community.

Sam Howse, Bunny Moir, and dear old cats—you are remembered for the love, laughter, learning, and long journeys home.