adding text in a specific position in beamer

Question

I have this slide and I wish not to change the composition. I would like to add the author of the image in a specific position (the red rectangle), i.e. M.C. Escher, Relativity (1953)

\frame{\frametitle{Introduzione}
    \justifying
    \scriptsize
\vspace{-0.25cm}
Aggarwal, C. C., Hinneburg, A., Keim, D. A. 2001. \emph{On the surprising behavior of distance metrics in high dimensional space}. In International conference on database theory, pp. 420-434. Springer, Berlin, Heidelberg. (\emph{1859 citazioni su Google Scholar nel maggio 2021})
\vspace{-0.25cm}
% \vspace{-0.35cm}
\begin{figure}
    \centering
    \includegraphics[scale =0.155]{Escher.jpg}
\end{figure}
\vspace{-0.35cm}

Answer 1

This is perhaps one of the simplest methods.

\documentclass[11pt]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usetheme{Pittsburgh}

\usepackage{graphicx}
\usepackage{caption} % better control of captions
\captionsetup[figure]{textfont={scriptsize,it}}
\begin{document}
\begin{frame}
    \frametitle{Introduzione}
    {\scriptsize    Aggarwal, C. C., Hinneburg, A., Keim, D. A. 2001. \emph{On the surprising behavior of distance metrics in high dimensional space}. In International conference on database theory, pp. 420-434. Springer, Berlin, Heidelberg. (\emph{1859 citazioni su Google Scholar nel maggio 2021}) }
\begin{figure}
    \begin{minipage}[b]{0.80\textwidth}
        \centering
    \includegraphics[width=0.7\textwidth,  height=0.6\textwidth]{example-image}
    \end{minipage}\hfill
    \begin{minipage}[b]{0.2\textwidth}      
        \caption*{M.C. Escher, Relativity (1953)} \label{fig:01}
    \end{minipage}
\end{figure}

\end{frame}
\end{document}

See also https://tex.stackexchange.com/a/29163/161015

Answer 2

Using an \rlap after the \includegraphics, on a full-width figure will ensure that the image remains centered. As presently configured, the baselines of the image and the annotation are the same.

\documentclass[11pt]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usetheme{Pittsburgh}

\usepackage{graphicx}
\usepackage[usestackEOL]{stackengine}
\usepackage{caption} % better control of captions
\captionsetup[figure]{textfont={scriptsize,it}}
\begin{document}
\begin{frame}
    \frametitle{Introduzione}
    {\scriptsize    Aggarwal, C. C., Hinneburg, A., Keim, D. A. 2001. \emph{On the surprising behavior of distance metrics in high dimensional space}. In International conference on database theory, pp. 420-434. Springer, Berlin, Heidelberg. (\emph{1859 citazioni su Google Scholar nel maggio 2021}) }
\begin{figure}
        \centering
    \includegraphics[width=0.6\textwidth,  height=0.5\textwidth]{example-image}

\rlap{\quad\scriptsize\Longstack[l]{M.C. Escher\Relativity (1953)}}
    \end{figure}
\end{frame}
\end{document}

Answer 3

If you want to add an object at an arbitrary position in the slide, you can use tikz with overlay option:

\documentclass[11pt]{beamer}
\usepackage{graphicx}
\usepackage{ragged2e}
\usepackage{tikz}
\begin{document}
\begin{frame}{Introduzione}
  \justifying
  \scriptsize 
  \vspace{-0.25cm}
  Aggarwal, C. C., Hinneburg, A., Keim, D. A. 2001. \emph{On the surprising 
  behavior of distance metrics in high dimensional space}. In International 
  conference on database theory, pp. 420-434. Springer, Berlin, Heidelberg. 
  (\emph{1859 citazioni su Google Scholar nel maggio 2021})
  \vspace{-0.25cm}
  \begin{figure}
    \centering
    \includegraphics[width=0.7\textwidth,  height=0.6\textwidth]{example-image.png}
  \end{figure}
  \vspace{-0.35cm}
  %
  \tikz[overlay, remember picture,
    shift=(current page.south west),
    x=(current page.south east), y=(current page.north west),
  ]{
    \node[align=left]at (0.9,0.1) {M.C. Escher,\Relativity (1953)}; 
    % Optional help grid lines
    %\draw[step=.1, opacity=0.3, thick, red] (0,0) grid (1,1);
  }
\end{frame}
\end{document} 

The coordinates (0.9,0.1) are absolute with respect to the below left corner to the slide and are normalized (coordinate (1,1) is the upper right corner)

You can uncomment he code below Optional help grid lines in order to draw grid lines for guessing that coordinates:

Of course, you can define new commands for this:

\newcommand{\posabs}[2][]{
  \tikz[overlay, remember picture,
    shift=(current page.south west),
    x=(current page.south east), y=(current page.north west),
    #1
  ]{#2}
}
\newcommand{\postextabs}[4][align=left]{
  \posabs{\node[#1] at (#2,#3) {#4};}
}

This add tikz code at an arbitrary position:

\posabs[red]{\node[circle, fill=red] at (0.5,0.5) {};}

This add a text node at an arbitrary position:

\postextabs[red]{0.5}{0.5}{\huge !!}