Isolating and saving an image in a .vob file

Years ago my relatives sent slides to a Dr. DVD who is now out of business. What we got back were CD's with slide shows in a .vob format. They play nicely but I would like to grab a slide and not the whole show for duplication. If I try and image capture while I pause the show, I cannot grab the image. Any suggestions on how this can be done? Many thanks...Rat