I Spy, the brand based on the photography-based seek-and-find books with images by Walter Wick and rhymes by Jean Marzollo, marks its 20th anniversary year starting this month. This past Monday Scholastic launched a year-long birthday bash with a variety of promotional activities under the “I Spy a Celebration” banner. While the core of the property is the eight original books published in the 1990s—from I Spy: A Book of Picture Riddles in 1992 to I Spy Treasure Hunt in 1999—the brand is still going strong today with new spin-off publishing, interactive gaming, licensed consumer products and more.

It all started in the early 1980s when Marzollo, then editor of Scholastic’s Let’s Find Out magazine, received a promotional piece from Wick, featuring a photo of hardware on a white background. She commissioned a poster of fasteners in a similar style, which led over the next decade to many more assignments and ultimately a request from Scholastic’s publishing division for a children’s book. “It was all because of a picture I had done just by cleaning my studio,” Wick says.

Wick brought his expertise in visual games and photography to the project, while Marzollo contributed her long experience in children’s education and writing. For the first book, Wick photographed objects he thought would be visually interesting and go well together, keeping lists of objects to make sure there were plenty of rhyming words. He contacted Marzollo when he had questions about child-appropriate content, such as “Is it OK to have a fish hook in there?” (It was.) With each subsequent book, the process became more collaborative. “We worked more on the concepts and the pros and cons of different thematic approaches,” Wick recalls.

Marzollo wrote the rhymes in dactylic tetrameter, the poetry meter familiar from children’s stories such as Old Mother Hubbard and The Night Before Christmas. “It’s light, vivid and active, and it’s great for kids,” she says. Later, she discovered that dactylic tetrameter is also the basis for rap. “One time some kids came up to me in a school and said, ‘We love to rap I Spy,’ and it was true, every single riddle in I Spy, they could rap. I do it now when I visit schools and they laugh, but it really works.”

I Spy appeals to all ages—autistic children and English language learners have really taken to the books, Marzollo says—and solving the puzzles is equally challenging for young and old alike. But the sweet spot is age five. “The photographs are so sophisticated that they draw in both the parents and the kids, but it’s really written for the kindergartner in all of us,” Marzollo explains. “Solving the riddles provides this enormous satisfaction. Kids know, ‘If I work hard, I will win.’ ”

Wick’s creative process changed over time, from photographing found objects to creating and lighting environments, dioramas and mini-landscapes, building props, and seeking objects that fit the theme. “People are very surprised to see how much goes into this,” he says. “They think the scenes exist and I was fortunate enough to find them. But there’s a little bit of theater involved.”

In addition to solving the riddles and finding the objects, children are able to analyze how the photos are made and how various contraptions work. “There’s a lot to think about and discuss,” Wick says. “When objects appear to be floating through the air and are done photographically, children, at ages where they can’t read, ask questions like ‘How do you get that to float in the air or balance like that?’ ”

All the spin-off books, which are written by Marzollo with the help of her two sons, are based in the world of the original eight books, which collectively contain more than 100 pictures and somewhere between 5,000 and 10,000 objects. “I think of it as a giant kindergarten classroom filled with things for kids to explore,” Marzollo says. Spin-off titles to date include five Challengers, 15 Readers, eight board books and three miscellaneous titles (I Spy Phonics Fun Boxset, I Spy A to Z, and I Spy A Christmas Tree). All told, 42 million I Spy books are in print.

Ellie Berger, president of Scholastic Publishing Group, notes that the spin-offs retain the quality of the original material, but each format is targeted to a different age. “It’s not one-size-fits all,” she says, citing the 6x9 readers as particularly successful. “The kids already know the game play, and it’s fun for them when they can master the books themselves.”

“Everything about I Spy was really new and different from a publishing process point of view,” says Deborah Forte, president of Scholastic Media and executive v-p of Scholastic Inc, who has overseen I Spy’s interactive and entertainment extensions. “It’s one of those very unusual book projects. It’s not just a book, it’s a game; it’s for families and not just children; unlike a novel, it’s shared and there’s this sense of community. As soon as you picked up the book you could see it could be extended into immersive experiences of all kinds.”

Marzollo and Wick worked with the Scholastic Media division and outside licensees in the early years to brainstorm what the world of I Spy should look like in different forms. “We wanted to make sure the spin-off products had the flavor of the I Spy books and kept the integrity,” Wick says. “We spent a lot of time with the licensees and we were able to create a culture of understanding.”

“The I Spy experience on any other platform will still be I Spy,” agrees Daisy Kline, Scholastic Media’s v-p marketing and brand management. “Our partners truly understand the brand, and that’s what’s made it successful. We also have such a wide array of constituencies—kids, parents, teachers and grandparents—who are fans of the brand. I Spy has endured because of that, and because of Walter and Jean’s unique take that is so original and timeless.”

I Spy interactive games in all platforms, from CD-ROM to mobile apps to Nintendo’s Wii, have been on the market for over 10 years, as has the I Spy television show on HBO Family. Briarpatch, now in its 18th year as an I Spy licensee, has shipped over 10 million units of more than 60 board and card games and puzzles. “I Spy has such a striking play pattern of read a riddle, solve a riddle, and seek and find,” says Briarpatch general manager Marc Shinderman. “We liked it right away and it was an immediate success.”

To mark the anniversary, the “I Spy a Celebration” promotion will encompass initiatives throughout all of Scholastic’s divisions, generating 200 million incremental impressions, according to Kline. The campaign includes national advertising to invite participation in the largest-ever game of I Spy, which took place this past Monday; several live events in New York; and two anniversary sweepstakes, one in conjunction with the launch of I Spy fruit snacks and the other through Scholastic Book Clubs. I Spy Spectacular: A Book of Picture Riddles is being released this month, followed by an I Spy Spectacular game from Briarpatch in June. Additional plans for 2011 include two readers and a board book and two more console games, among other initiatives.