Making a sill photo from a dvd
the easy way, well I hope anyway, would be to take a screenshot with the movie paused where you want it. now, the DVD Player application does not let you take screenshots when it's open. so you'll need an additional application, either to playback the movie or take the screenshot.
so, it would be easier & better to tell you to get another video player. it's free & pretty simple to install. it's called VLC & can be found at http://videolan.org
once installed, play the disc using VLC & pause where you would like to take a picture. I think using the arrow keys will nudge frame to frame when paused, which is similar to quicktime. there's plenty of faq stuff on their site to help with VLC if you need more info.
& here's how to do screenshots in Mac OS - http://take-a-screenshot.org/ click the Mac tab.