Is there a simple way to get book cover in JSON format from ISBN using Google Book API?
You can use the isbn:
query, like this:
https://www.googleapis.com/books/v1/volumes?q=isbn:0771595158
This will return a proper JSON response containing either the book information or an error description if the ISBN is not found.
If you are looking for an answer for a Ruby (Rails, Sinatra or Console) answer on how to get a conver image or for that matter any detail available through the Google Books API, I think GoogleBooks gem is a good place to start.
For example, for the same scenario:
Install the gem
gem install googlebooks
Use the gem
require 'googlebooks'
GoogleBooks.search('isbn:9781443411080').first.image_link
first
because it returns a collection of books.