Beamer: How To Include Logo In Every Slide?

Bottom right is easy:

\documentclass{beamer}

\logo{\includegraphics[width=.1\textwidth]{example-image}}

\begin{document}

\begin{frame}
    abc
\end{frame} 

\end{document}

And with a dirty hack, it can be moved to the left:

\documentclass{beamer}

\logo{\includegraphics[width=.1\textwidth]{example-image}\hspace*{.88\paperwidth}}

\begin{document}

\begin{frame}
    abc
\end{frame} 

\end{document}

I found out that this is the best solution:

% Method to add an item that will appear in every slide
\addtobeamertemplate{footline}{%
  \setlength\unitlength{1ex}%
  \begin{picture}(0,0) 
    % \put{} defines the position of the frame
    \put(140,6){\makebox(0,0)[bl]{
    \includegraphics{figures/image1.png}
    \includegraphics{figures/image2.png}
    \includegraphics{figures/image3.png}
    }}%
  \end{picture}%
}{}

Surely many people come here wanting to add the logo at the top-right corner. For that, use this:

\setbeamertemplate{headline}{\hfill\includegraphics[width=1.5cm]{example-image}\hspace{0.2cm}\vspace{-1cm}}

Adjust the parameters (width, hspace, vspace) accordingly.