We use this book as a training manual for new developers and have had no problems with the content. In fact, one developer raves that it is the best book he’s ever read when it comes to programming books.
I would suggest you take a second look at your code and make sure you’ve implemented it just as the book instructs.
The NoMethodErrorr for ‘image_url’ you see is an indication that rake db:migrate did not work. Check your database for the tables and columns.