Modifying enumerate items in beamer - insert graphics while generating labels

Question

I'm trying to make myself a beamer template with modified bullets for enumerate and itemize. I have a pdf image of the bullet point that I would like to use. I already have a working solution for itemize, but using the same approach

\newcommand{\bpebble}[0]{\includegraphics[height=1.3 ex]{./k_bluepebble.pdf}}
\setbeamertemplate{enumerate items}{\bpebble}

the numbering vanishes making the enumerate and itemize environments essentially indistinguishable. I've seen a near-satisfactory solution Use ball items in enumerate list with enumitem package in that it modifies the item in front of each enumerate list entry and superimposes a number on top of it, however this uses pgfplots and not an inserted pdf figure.

So, I'm seeking a way to include a pdf graphic into the list bullets and lay a number on top of it.

Answer 1

Here's one possibility allowing you to insert an image as background for the counters in enumerate environments; the code illustrates the simple procedure up to level three of nesting (the maximum nesting level for beamer). The main command is \bpebble with three mandatory arguments:

\bpebble{<optionf for \includegraphics>}{<image file>}{<counter to be used over the image>}

The complete code:

\documentclass{beamer}
\usepackage{tikz}

\newcommand\bpebble[3]{%
  \tikz{
  \node[inner sep=0pt] 
    (image) {\includegraphics[#1]{#2}};%
  \node[inner sep=0pt] 
    at (image.center) {#3};%
  }
}

\setbeamertemplate{enumerate item}{\bpebble{height=2ex}{papiro}{\insertenumlabel}}
\setbeamertemplate{enumerate subitem}{\bpebble{height=1.8ex}{bricks}{\insertsubenumlabel}}
\setbeamertemplate{enumerate subsubitem}{\bpebble{height=1.6ex}{scroll}{\insertsubsubenumlabel}}

\setbeamercolor*{enumerate item}{fg=white} 
\setbeamercolor*{enumerate subitem}{fg=white} 
\setbeamercolor*{enumerate subsubitem}{fg=black} 

\begin{document}

\begin{frame}
\begin{enumerate}
\item First.
\item Second.
  \begin{enumerate}
  \item First.
  \item Second.
    \begin{enumerate}
    \item First.
    \item Second.
    \end{enumerate}
  \item Third.
  \end{enumerate}
\item Third.
\item Fourth.
\end{enumerate}
\end{frame}

\end{document}

The result: