This is a great little freeware app that you can find by running a search on the SourceForge website:

If you have a video playing or paused, you can use the "Save Picture" menu item under the File menu. What's better, is that MPC lets you go to a specific time index (down to the second) or even a specific frame if you know which one you want. And it will play DVDs provided you have some sort of DVD decoder installed or it's an unencrypted DVD.