hbox out of margin, beamer

Question

I wanna put a round image in a presentation il LaTeX out from the margin. I would like to show it just as a 1/4 of the image in the left bottom corner.

I tried:

\begin{frame}
  \tableofcontents
  \hbox to -35pt{
    \vbox to 35pt{
        \includegraphics[width=4cm,keepaspectratio]{img/prova}\hfil
    }
   }
\end{frame}

but the image goes under the bottom margin (so changing the value of \vbox the image go down or up). I also tried to change the value of the \hbox also with positive values but nothing happen.

Answer 1

By giving a bb option to \includegraphics you can specify the bounding box of the image, and so how much latex thinks the image occupies on the page. This is independent of the actual size of the image. You can let the image spill over, or you can clip it to the bounding box. Both possibilities are illustrated below:

\documentclass{beamer}

\usepackage{mwe}

\begin{document}
\begin{frame}
  \lipsum[1]
  \includegraphics[width=3cm,bb= 10 150 180 250]{example-image-a}
\end{frame}
\begin{frame}
  \lipsum[1]
  \includegraphics[width=3cm,bb= 10 150 180 250,clip]{example-image-a}
\end{frame}
\end{document}

The four parameters are the x- and y-coordinates of the bottom left hand corner of the selected part of the image, followed by the x- and y-coordinates of the upper right hand corner. Thus the above options select a rectangle in the image that is (180-10)x(250-150) = 170 x 100. The units used are bp, 1in = 72bp. See the documentation of the graphicx package for more details, and other options, including viewport and trim.

To ensure the image appears at the bottom of the page, you can just precede it with

\vspace{0pt plus 1fill}