If you can get used to specifying figures with commands, rather than environments, boxhandler will solve this, assuming you mean left-align to the figure and not the margin. (It can left align to margin, too, but you don't need boxhandler for just that)
\documentclass{article}
\usepackage{boxhandler}
\begin{document}
By default, boxhandler gives this
\bxfigure[ht]{This is the caption which, by default is idented wrt the
figure identifier}
{\rule{3in}{2in}}
But by changing the caption style with \verb|\captionStyle{n}{l}|, one
gets the following:
\captionStyle{n}{l}
\bxfigure[ht]{This is the caption which, by default is idented wrt the
figure identifier}
{\rule{3in}{2in}}
\end{document}
