There is an art pack in the digital CE, and the Source Hunder DLC (basically a standard edition to CE upgrade), which I assume is the same as the digital art book.

With the kickstarter rewards the art book was a separate reward from the CE. All the tiers with a physical CE ($95+) also included a physical art book, but at $75 you could get the standard physical edition of the game and a digital version of the art book.