I want to generate a PDF with our department logo in it. When I try to use the WickedPdf class in my controller (using the method described at <https://github.com/mileszs/wicked_pdf>):

```
def some_action
  image_tag_string = image_tag('logo.jpg')
  pdf = WickedPdf.new.pdf_from_string(image_tag_string)

  save_path = Rails.root.join('testpdfs','logotest.pdf')
  File.open(save_path, 'wb') do |file|
    file << pdf
  end
end

```

...the application saves the PDF to the target directory, but it has a blue-and-white '?' mark where the image should be.

If I do this instead:

```
  image_tag_string = wicked_pdf_image_tag('logo.jpg')
  pdf = WickedPdf.new.pdf_from_string(image_tag_string)

```

I get the following error: 

```
NoMethodError:
   undefined method `wicked_pdf_image_tag' for #<...

```

It would appear that my Rails app is also missing / not linking to a helper file belonging to the wicked-pdf gem.

Answers to similar questions on StackOverflow recommend writing a custom "image-tag" helper to locate the image or installing wkhtmltopdf. For me, image-tag shows the logo just fine when placed in a View (whatever.html.erb). "logo.jpg" is already located in both the asset pipeline and #{RailsRoot}/public/images. Finally, I am using wkhtmltopdf 0.9.9, wicked-pdf 0.11.0, and rails 4 on Ubuntu 14.04.

In a nutshell - what am I doing wrong that causes WickedPDF to fail to render the image?