The information about this project is quite messy. So here is the official info from the DVD itself.

DVD "The Legendary Crocodile Jake" Began with a Single Picture Book...
In April 2001, an unusual picture book titled The Legendary Crocodile Jake was released.
The book presents a collection of eyewitness accounts and illustrations documenting encounters with Jake, gathered by the freelance journalist Shannon K. Isuyama as he traveled the world interviewing people who claimed to have met the mysterious creature.
In reality, however, there is no such person as Shannon K. Isuyama. He is a fictional character created by Shinichi Inudō, who is credited in the book as its translator. Accordingly, the eyewitness testimonies themselves are also fictional works written by Inudō. Likewise, the illustrations were drawn by Noriko Yamakusa, who is credited as the book's illustrator.
In fact, a nearly complete prototype had already been privately produced in 1985. For that reason, the story is set entirely during the 1980s. After sixteen years—and various experiences along the way—it was finally published as the picture book you see today.

Based on the picture book, a television adaptation aired on TV Tokyo from July through December 2001. Broadcast every Sunday at 10:48 p.m. as a five-minute program, the series ran for a total of 25 episodes.
In the TV version of The Legendary Crocodile Jake, Jun Murakami plays Shannon K. Isuyama, the supposed author of the picture book. The program follows him as he interviews people who claim to have encountered Jake. The eyewitness testimonies from the book are performed by actors, while Jake himself is depicted through animation.
The series was written and directed by Shinichi Inudō, who also created the original picture book. The animation was produced by animator Kōji Yamamura.
Thanks to its original concept, unique casting, and high-quality animation, the program went on to achieve cult status.
The DVD edition of The Legendary Crocodile Jake includes newly added scenes of Shannon's travels and his monologues. It also re-edits the individual television episodes into a single road movie following Shannon K. Isuyama as he journeys in search of eyewitness accounts of Jake.