I'm not sure that description is the best way do to this; I'd use
\begin{flushleft}
\sbox0{\includegraphics{pict1}}
\raisebox{-.5\height}{\usebox0}\quad
\begin{minipage}{\dimexpr\textwidth-\wd0-1em}
Description
\end{minipage}
\end{flushleft}
The main problem is in fact that the description text height is not known in advance. This could be easily made up into a new environment.
Here's an example:

If your descriptions are only one line long, then a different and simpler approach can be used.
\documentclass{article}
\usepackage{enumitem}
\usepackage[export]{adjustbox}
\begin{document}
\begin{description}[labelwidth=3cm]
\item[{\includegraphics[valign=c,width=2.5cm]{a}}] Description a
\item[{\includegraphics[valign=c,width=1.5cm]{b}}] Description b
\item[{\includegraphics[valign=c,width=2cm]{b}}] Description c
\end{description}
\end{document}
Adjust the parameters to description to suit you. The key is valign=c provided by adjustbox.

\itemis found. A solution simply with\itemrequires to know more about your possible text and also about the width of the labels/pictures and relative alignment of the texts. – egreg May 04 '12 at 22:48