Here's an interesting storybook I came across at a yard sale. "Casper the Friendly Ghost in Ghostland" was published in 1969 with story and art by the Harvey Cartoon Studios.Although it's called "..in Ghostland", most of the story takes place in the old west where Casper, Spooky and Nightmare take care of horse rustlers.
The artwork seems to have been done by cartoonist Warren Kramer who handled the artwork for many other Harvey Comic titles. The illustrations appear to be painted unlike the comic book art which gives it more of a storybook feel.
Check out these great images from this Wonder Books story...