Prawn is an excellent PDF generation library for ruby, and we use it for all our PDF needs at work. Their manual is some of the best documentation I have read. Recently, I needed to set a different background image on every page of a PDF I was generating. The prawn documentation, while good, only shows how to use a background image for the whole PDF:

img = "some/image/path.jpg"

Prawn::Document.generate(filename, background: img, margin: 100) do |pdf|
  pdf.text 'My report caption', size: 18, align: :right
end

So, I decided to dig into their source code to see how they rendered the background image. After a short search I found what I needed. Turns out, this works for rendering multiple different background images! In prawn you can call pdf.start_new_page to start a new page, and on each new page I would call the following to set the new background for that page:

background_image_path = 'some/path/for/this/page.jpg'
pdf.canvas do
  pdf.image(background_image_path, scale: 1, at: pdf.bounds.top_left)
end

I was able to generate the PDF with different background images perfectly with this code.