\def\chapauth#1{\gdef\@chapauth{#1}}
\def\@chapauth{}

\def\chapimg#1#2{\gdef\@chapartist{#1}\gdef\@chapimg{#2}}
\gdef\@chapimg{}
\gdef\@chapartist{\@empty}

\def\@makechapterhead#1{%
  \ifx \@chapimg \@empty
    \vspace*{50\p@}%
      {\parindent \z@ \raggedright \normalfont
      \ifnum \c@secnumdepth >\m@ne
        \if@mainmatter
          \huge\bfseries \@chapapp\space \thechapter
          \par\nobreak
          \vskip 20\p@
        \fi
      \fi
      \interlinepenalty\@M
      \Huge \bfseries #1\par\nobreak
      \ifx\@chapauth\@empty
        % Nothing
      \else
        \vskip 10\p@
        \Large \bfseries by \@chapauth\par\nobreak
      \fi
      \vskip 40\p@
      }
  \else
    \thispagestyle{empty}
    \hbox{}\vfill
    \noindent
    \includegraphics[width=\textwidth]{\@chapimg}
    \par\nobreak
    \hfill Artwork by \@chapartist
    \par\nobreak
    \vfill\hbox{}
    \addcontentsline{lof}{figure}{Chapter art by \@chapartist}
  \fi
  \chapauth{}
  \chapimg{}{}
}