Custom chapter with image

I would like to modify the \chapter{} command such that I can include a (fixed height) image in the following sense (quick sketch I made in LibreOffice) with an orange border around it:

Is this possible using TikZ?

//edit: Here is what I get (the aspect ratio is messed up, sure, but that will be OK later on because I will select a picture that works):

The MWE is here:

\documentclass[12pt]{book}

\usepackage{lipsum}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{titlesec}
\titleformat{\chapter}[display]
{\huge\bfseries}
{\makebox[0cm][r]{\huge\bfseries}\thechapter.\hskip15pt}% label
{0pt}
{\tikz[remember picture,overlay]\node[inner sep=0pt] at ($(current page.north) + (0,-2cm)$) {\includegraphics[width=\paperwidth, height=4cm]{example-image-a}};
}
[]
\begin{document}
\chapter{A Chapter}
\lipsum[4]
\end{document}


There are the following problems:

• There is a weird line break between the chapter number and the title. Why?
• If I adjust the height of the image to be, say, 8cm, it will cover the chapter numbering etc. How can I make sure it is always after the end of the image?
• Packages titlesec, or with memoir or change \@makechapterhead etc. No need for TikZ, in my point of view – user31729 Dec 9 '17 at 21:44
• Can you point me to a MWE? – Jens Dec 9 '17 at 21:53
• Maybe tex.stackexchange.com/questions/159978/… could help. – user36296 Dec 9 '17 at 22:46
• @samcarter: see my edited question above, it is almost what I want, but there are some issues. – Jens Dec 10 '17 at 0:01
• Do you really need to draw the image using TiKz? Must it be a vector image? Is your book math/academic? Is your book an E-book? If the answer is no to all, then consider using the novel class. It specially deals with fixed-height chapter starts. But images must be raster grayscale for print to paper. You would create your image in (for example) GIMP. – user139954 Dec 10 '17 at 0:37

With the overlay, the box will be essentially invisible to TeX as far as the space it occupies is concerned.

\documentclass[12pt]{book}
\usepackage{graphicx}
\usepackage{titlesec}
\usepackage{lipsum}

\titleformat{\chapter}
{\huge\bfseries\printcurrentpicture}
{}
{0pt}
{\makebox[0cm][r]{\thechapter.\hspace{15pt}}}
\titlespacing{\chapter}{0pt}{0pt}{20pt}
\newcommand{\printcurrentpicture}{%
\moveleft\dimexpr\oddsidemargin+1in\vbox{%
\hbox{%
\includegraphics[width=\paperwidth]{\thechapterpicture}%
}
\vspace{20pt}
}%
}
\newcommand{\chapterpicture}[1]{%
\def\thechapterpicture{#1}%
}

\begin{document}

\chapterpicture{example-image-a}
\chapter{A Chapter}
\lipsum[4]

\end{document}


You'll have to define a suitable version for unnumbered chapters.