Logo behind section labels in sidebar

Question

I have found a few questions talking about:

• placing images behind text in beamer, e.g. (1) (2)
• adding logos to a beamer presentation, e.g. (3)
• customizing a sidebar in beamer, e.g. (4)

But I haven't quite figured out how to get a template with an image behind the section headings in a sidebar.

So what I want is the following:

1. That the \section and \subsection labels show up as clickable links in a sidebar
2. That a logo appears in the sidebar.
3. That the logo does not move around when \section and \subsection are added.
4. That the image is placed behind the text.

How can this be achieved?

To illustrate what I want, I created a quick mockup, see below.

Answer 1

You can use the sidebar canvas <which ever side> template to place the logo behind the text of the sidebar:

\documentclass{beamer}
\usetheme[left]{Goettingen}
\usepackage{tikzlings}

\makeatletter
\setbeamertemplate{sidebar canvas left}{%
\color{gray!20!white}%
\rule{\beamer@sidebarwidth}{\paperheight}

\vspace*{-.6\paperheight}
\begin{tikzpicture}
\pgfsetfillopacity{0.4}
\begin{pgftransparencygroup}
    \penguin
\end{pgftransparencygroup}
\end{tikzpicture}
}
\makeatother

\begin{document}
\section{sec 1}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}

\section{sec 2}
\begin{frame}
abc
\end{frame}
\end{document}