I am using TeXLive 2011 on Windows 7. The following solution has been tested on the production and works without problem. If you use different operating system then my answer might not work. There are 3 steps as follows:
Step 1 : Create a batch file
The batch file has a job to create a temporary plain text file that contains the list of file names (in your context, the PNG file names).
Let MakeFileList.bat be the name of the batch file. It contains the following codes:
rem %1 represents the path relative to the main input file.
set curdir=%CD%
cd %1
dir /b *.png > %curdir%\FileList.temp
For simplicity (to avoid editing PATH system variable), save the batch in the same directory in which your TeX input file is saved.
Step 2 : Create the TeX input file
Now you write the TeX input file as follows.
\documentclass{article}
\usepackage{graphicx}
\newread\reader
\makeatletter
\newcommand\Import[2][1]{%
\immediate\write18{MakeFileList #2}%
\openin\reader=FileList.temp\relax
\loop
\read\reader to \x
\unless\ifeof\reader
\filename@parse{\x}
\begin{figure}
\centering
\includegraphics[scale=#1]{#2\filename@base}
\caption{\filename@base}
\label{fig:\filename@base}
\end{figure}
\repeat
\closein\reader}
\makeatother
\begin{document}
\Import[0.5]{Images/}
\end{document}
The code above will execute the batch, the batch prepares the list of PNG file names, the remaining codes iterate the list and sandwiches each image with figure.
\Import takes 2 arguments. The first argument, which is optional, is used to scale the imported graphics. The second mandatory argument represents a path.
Step 3: Compile with -shell-escape enabled
Let inputfile.tex be the name of TeX input file. Compile the input file with pdflatex -shell-escape inputfile.tex.