\Preamble{xhtml}
\Configure{graphics*}
    {jpg}
    {%
        \Picture[pict]{\csname Gin@base\endcsname .jpg
              \space width="\the\dimexpr \expandafter\csname Gin@req@width\endcsname * 1.5"}%
        \special{t4ht+@File: \csname Gin@base\endcsname.jpg}
    }
\Configure{graphics*}
    {png}
    {%
        \Picture[pict]{\csname Gin@base\endcsname .png
            \space width="\the\dimexpr \expandafter\csname Gin@req@width\endcsname * 1.5"}%
        \special{t4ht+@File: \csname Gin@base\endcsname.png}
    }
\begin{document}
\EndPreamble