Per-page backgrounds in LaTeX

Question

I have a sequence of images, img1.png, img2.png, img3.png, ... I would like img1.png to appear in the background of page 1 of my LaTeX document, and img2.png to appear in the background of page 2 of my document, and similarly for img3.png and so on.

I have more images than pages. There is also a cover page and table of contents, which I am ignoring for the sake of argument. Note that these images are all different, and in particular they do not repeat e.g. with every odd or every even page.

Any ideas? Thank you.

Answer 1

Welcome to TeX.SE! With the following code, you can define the image sequence wherever you want (even change it mid-document) like so:

\setimages{example-image-a, example-image-b, example-image-c}

It has wrap-around behavior if you have more pages than images in the image sequence (I know you didn't ask for it, but that was a rather cheap addition). You probably won't care, but \setimages respects TeX grouping too.

\documentclass{article}
\usepackage{eso-pic}
\usepackage{graphicx}
\usepackage{xparse}
\usepackage{lipsum} % provides dummy text for demonstration purposes

\ExplSyntaxOn

\seq_new:N \g_jim_images_seq

\cs_new_protected:Npn \jim_use_as_bg_picture:n #1
  {
    \AtPageLowerLeft
      { \includegraphics[width=\paperwidth, height=\paperheight] {#1} }
  }

\cs_generate_variant:Nn \jim_use_as_bg_picture:n { x }

\NewDocumentCommand \setimages { m }
  { \seq_set_from_clist:Nn \g_jim_images_seq {#1} }

\NewDocumentCommand \setbgpicforcurrentpage { }
  {
    % Compute wrapped-around 0-based index in \g_jim_images_seq
    \int_set:Nn \l_tmpa_int
      { \int_mod:nn { \the\value{page} - 1 } { \seq_count:N \g_jim_images_seq } }
    % Set it as the current page background
    \jim_use_as_bg_picture:x
      { \seq_item:Nn \g_jim_images_seq { \l_tmpa_int + 1 } }
  }

\ExplSyntaxOff

\AddToShipoutPictureBG{\setbgpicforcurrentpage}

% Use example-image-a for page 1, example-image-b for page 2, example-image-c
% for page 3, etc. This respects TeX grouping and can be reset mid-document.
\setimages{example-image-a, example-image-b, example-image-c}

\begin{document}
% Current image sequence: a, b, c, a, b, c, a ...
\lipsum
\lipsum
\lipsum
\lipsum
\lipsum
% Change the image sequence to: a, b, a, b, a, b, a...
\setimages{example-image-a, example-image-b}%
\lipsum
\lipsum
\lipsum
\end{document}