Over the years I have used many small applications to extract metadata from images but none of them were as versatile as Image-ExifTool by Phil Harvey. It support just about any image or video file format your can imaging. And a nice thing is that it is implemented in Perl so that one can easily use it to build a script. And it works cross-platform which is important for me who move between three operating systems on a daily basis.
This is all it takes to extract all metadata from a file:
