Reference to a entry in bibliography without generating it

Question

In review articles it often happens that a figure is taken from another document which is mentioned in the \caption by a \cite macro. If such a caption preceeds the first occurence of the corresponding \cite in the text, the number is increased when the caption is processed by TeX. Since the reader does not read the caption first, but will proceed with the main text until the next paragraph or headline, the numbering in the text has a gap.

Thus, I would like to reference an entry in the bibliography without creating it. a simple \ref does not work. Any ideas?

Update: The following exmaple produces the desired numbering in the text, but no citation in the caption. As soon as I use the comment version in the \caption, the numbering is not as I want it. (Don'T forget to re-run bibtex while testing).

\begin{filecontents}{./mybib.bib}
@misc{foo,
  author={Foo},
  title={Foo},
}
@misc{bar,
  author={Bar},
  title={Bar},
}
@misc{baz,
  author={Baz},
  title={Baz},
}
\end{filecontents}

\documentclass{article}
\usepackage[super]{natbib}
\bibliographystyle{unsrtnat}
\begin{document}

\begin{figure}
  \caption{Taken from Foo\ref{foo}}
  %  \caption{Taken from Foo\cite{foo}}
  \label{fig:foo}
\end{figure}

Bar\cite{bar} and baz\cite{baz} have done some fascinating research,
which is best summarized as shown in Figure~\ref{fig:foo} (originally 
by Foo\cite{foo}).

\bibliography{./mybib}
\end{document}

Answer 1

Here is a solution that works with natbib when loaded with the super option; another one that works with standard LaTeX, as well as with natbib and the numbers option, is at the bottom.

\begin{filecontents}{./mybib.bib}
@misc{foo,
  author={Foo author},
  title={Foo title},
}
@misc{bar,
  author={Bar},
  title={Bar},
}
@misc{baz,
  author={Baz},
  title={Baz},
}
\end{filecontents}

\documentclass{article}
\usepackage[super]{natbib}
\bibliographystyle{unsrtnat}

% we patch the \bibcite macro to store the number of the
% citation     
\usepackage{xpatch,xstring,etoolbox}
\makeatletter
\xapptocmd{\bibcite}{%
    \StrLeft{#2}{1}[\knall]%
    \StrRemoveBraces{\knall}[\peng]
    \global\csedef{defcite@#1}{\peng}
}{}{}

% the \deferredcite macro calls up the number stored above, if available;
% it does not itself cause a citation to be created. 
\newcommand{\deferredcite}[1]{%
\ifcsdef{defcite@#1}{\textsuperscript{\csuse{defcite@#1}}}{?}}
\makeatother

\begin{document}

\begin{figure}
    \caption{Taken from Foo\deferredcite{foo}}
  \label{fig:foo}
\end{figure}

Bar\cite{bar} and baz\cite{baz} have done some fascinating research,
which is best summarized as shown in Figure~\ref{fig:foo} (originally 
by Foo\cite{foo}).

\bibliography{./mybib}
\end{document}

Here a solution for standard LaTeX without natbib. Output is identical, except that in-text citations are in brackets rather than as superscript.

\documentclass{article}
\bibliographystyle{ieeetr} % to sort in order of appearance

\usepackage{etoolbox}
\makeatletter
\let\oldbibcite\bibcite
\renewcommand{\bibcite}[2]{%
    \oldbibcite{#1}{#2}%
    \global\csedef{defcite@#1}{#2}}

\newcommand{\deferredcite}[1]{~[\ifcsdef{defcite@#1}{\csuse{defcite@#1}}{?}]}

\makeatother

\begin{document}

\begin{figure}
  \caption[Taken from Foo]{Taken from Foo\deferredcite{foo}}
  \label{fig:foo}
\end{figure}

Bar~\cite{bar} and baz~\cite{baz} have done some fascinating research,
which is best summarized as shown in Figure~\ref{fig:foo} (originally 
by Foo~\cite{foo}).

\bibliography{./mybib}
\end{document}