You can use the background
package, but indeed it can be tricky to get the position right! Please see the following example in which I set a random picture as background at fixed margins using the hshift
and vshift
settings, following your image:
% !TeX program = xelatex
\documentclass{article}
\usepackage{background,lipsum}
\backgroundsetup{
scale=1,
color=black,
opacity=1,
contents={%
\includegraphics[%
height=\dimexpr\paperheight-2cm\relax, % double the vert. margin
width=\dimexpr\paperwidth-2cm\relax % double the horiz. margin
]{example-image-a}
},
angle=0,
position = current page.south west,
nodeanchor = south west,
hshift = 1cm, % horizontal margin
vshift = 1cm % vertical margin
}
\begin{document}
\lipsum[1-10]
\end{document}

background
? osl.ugr.es/CTAN/macros/latex/contrib/background/background.pdf