Well most people would load up the DVD in their DVD player software (such as PowerDVD or WinDVD) and get to the point they want, pause it and click the small Camera button, which takes a screenshot and puts it on the clipboard. You can then paste it into an image editor and manipulate and/or save it.

The screengrab on my software doesn't work however, so I have to rip the bit of video I want to my PC, then save it as an image sequence and pick the image I want. Takes a while, lol.