I do beamer presentations with lots of art. While I have not experimented to find minimum values, I get good results from anything 1024x768 pixels and up. This is flickr's "large" size.
I mention flickr because it's a good resource for this kind of thing. Do an advanced search and check the box for Creative Commons-licensed photos.
In case you want to keep looking for vector art, try these:
How about this: you have three commands:
\imagenode
for inserting the picture and setting up some dimensions
- the optional
\imagegrid
which helps putting the frame
\highlightbox
for drawing the frame
Code
\documentclass{beamer}
\usepackage{tikz}
\newcommand{\imagenode}[2][1]% [scale], filename
{ \node[above right,inner sep=0] (myimage) {\includegraphics[scale=#1]{#2}};
\path (myimage.north east);
\pgfgetlastxy{\myimagex}{\myimagey}
\pgfmathsetmacro{\myimagewidth}{\myimagex/28.453}
\pgfmathsetmacro{\myimageheight}{\myimagey/28.453}
}
\newcommand{\imagegrid}[4][help lines]% [options], steps, font, precision
{ \pgfkeys{/pgf/number format/.cd,fixed,precision=#4}
\foreach \x in {0,...,#2}
{ \draw[#1] (\x/#2*\myimagewidth,\myimageheight) -- (\x/#2*\myimagewidth,0) node[below] {#3\pgfmathparse{\x/#2}\pgfmathprintnumber{\pgfmathresult}};
\draw[#1] (\myimagewidth,\x/#2*\myimageheight) -- (0,\x/#2*\myimageheight) node[left] {#3\pgfmathparse{\x/#2}\pgfmathprintnumber{\pgfmathresult}};
}
}
\newcommand{\highlightbox}[8][densely dashed,thick]% [options], left, low, right, up, node options, node text, overlay spec
{ \only<#8>{\draw[#1] (#2*\myimagewidth, #3*\myimageheight) rectangle node[#6] {#7} (#4*\myimagewidth, #5*\myimageheight);}
}
\begin{document}
\begin{frame}
\begin{tikzpicture}
\imagenode[3]{book.png}
\imagegrid{10}{\tiny}{1}
\highlightbox[red,very thick]{0.1}{0.1}{0.7}{0.2}{blue}{red frame}{2}
\highlightbox{0}{0.3}{0.3}{0.7}{circle,draw,fill=green!50!gray,solid}{dash}{2-3}
\highlightbox[blue,fill=blue,fill opacity=0.3]{0.42}{0.23}{0.65}{0.74}{opacity=0.8,fill=orange,text opacity=1}{!?}{1,3}
\end{tikzpicture}
\end{frame}
\end{document}
Output
Best Answer
The following produces five slides: the first contains four images that are scaled down to fit within one frame, and the rest of the four slides each contains a bigger version of the images. By clicking on a smaller image, you can jump to the slide containing the bigger version of that image, and clicking the larger image will take you back to the initial slide of four images.