\chapter*{Bildquellen\markboth{Bildquellen}{Bildquellen}}
\addcontentsline{toc}{chapter}{Bildquellen}

\begin{itemize}
    \item[Abb. \ref{fig:s2}] $S^2$: Tom Bombadil, \href{http://tex.stackexchange.com/a/42865/5645}{tex.stackexchange.com/a/42865}
\end{itemize}