Background image in beamer slides

Question

In my presentation using Beamer, I want to use some image say village/river as a back ground in some slides. However I will write something in these slides also.

How can I do this?

Answer 1

You can also use \setbeamertemplate{background} {\includegraphics[width=\paperwidth,height=\paperheight,keepaspectratio]{background.jpg}} (where background.jpg is your picture).

A sample background:

Code

\documentclass{beamer}
\setbeamertemplate{background}
{\includegraphics[width=\paperwidth,height=\paperheight,keepaspectratio]{background.jpg}}


\begin{document}

\begin{frame}

\begin{exampleblock}{Test}
\begin{itemize}
\item First item.
\end{itemize}
\end{exampleblock}

\end{frame}

\end{document}

Edit

To answer the comment by the OP

Suppose I want to use african village (google image) as a back ground in some of my slides. But then written documents will be unclear. How one can convert the image as a water marking?

Here one can use the opacity option provided by tikz as

\setbeamertemplate{background canvas}{\begin{tikzpicture}\node[opacity=.1]{\includegraphics [width=\paperwidth]{example-image.pdf}};\end{tikzpicture}}

One can change the opacity values from 0 to 1 as per demand.

The code:

\documentclass{beamer}
\usepackage{tikz}
\setbeamertemplate{background canvas}{\begin{tikzpicture}\node[opacity=.1]{\includegraphics
[width=\paperwidth]{example-image.pdf}};\end{tikzpicture}} % only for the image: http://ctan.org/pkg/mwe
%      \setbeamertemplate{background}{\includegraphics[width=\paperwidth]{example-image.pdf}}
\begin{document}
\begin{frame}{Testing Background Image}
    Hello!
\end{frame}
\end{document}

Answer 2

Checking the beamer manual for background reveals the background canvas template:

The template is inserted “behind everything.” The template should typically be some TeX commands that produce a rectangle of height \paperheight and width \paperwidth.

\setbeamertemplate{background canvas}{<your code>}

<your code> can be an \includegraphics that is resized with width= or height=.
Since the exemplary image is already in an aspect ratio of 4:3, it suffices to only give one of these variables.

There is also the background template that is described by the manual, too:

The template is inserted “behind everything, but on top of the background canvas.” Use it for pictures or grids or anything that does not necessarily fill the whole background.

---

I did not see any difference between those two templates, so the following lines produced the same output:

\setbeamertemplate{background canvas}{\includegraphics[width=\paperwidth]{example-image.pdf}}
\setbeamertemplate{background}{\includegraphics[width=\paperwidth]{example-image.pdf}}

If you insert a more complex background (e.g. composed of a grid of images, background image only in one corner of the slides, …), you are better off using background instead of background canvas.

Code

\documentclass{beamer}
\setbeamertemplate{background canvas}{\includegraphics[width=\paperwidth]{example-image.pdf}} % only for the image: http://ctan.org/pkg/mwe
%      \setbeamertemplate{background}{\includegraphics[width=\paperwidth]{example-image.pdf}}
\begin{document}
\begin{frame}{Testing Background Image}
    Hello!
\end{frame}
\end{document}

Output