Rails 4 PaperClip ImageMagick Content Type Error for Images

I’m using ImageMagick and Paperclip for uploading images to my Rails app. It is working on my development machine, a Mac, but not here. When Paperclip tries saving different sizes of the images, ImageMagick give the error

Paperclip::Errors::NotIdentifiedByImageMagickError

I’m using Paperclip 4.2.1. In my Rails model I have:

has_attached_file :photo_image, :styles => { :medium => "330x250#", :small => "150x120#", :thumb => "120x100#" }, 
                                :url => "/system/dadverts/:attachment/:id/:style/:filename",
                                :path => ":rails_root/public/system/dadverts/:attachment/:id/:style/:filename",
                                :default_url => "300250ad.png"
                                
validates_attachment_content_type :photo_image, :content_type => /\Aimage/

In my production environment settings I have:

Paperclip.options[:command_path] = "/usr/local/bin/"

I’ve run sudo apt-get update a couple of times but this has not resolved the issue.

Any suggestions on what could be wrong would be appreciated.