Can you be a little more explicit about exactly what you want to do?
Since all your slideshows would have been created using photos etc. that were on your computer at the time each show was created, are you suggesting that at least some of those photos are no longer saved on your computer? Hence you are wanting to extract/recreate them from the show DVD(s)?
In timeline mode, load the VOB files into Photostory.
Position the timeline cursor at the image you want.
Select File, Export, Single frame as jpg.
Repeat steps 3 and 4 for every image you want.
However there is a fundamental issue - the image sizes will be the same as the DVD ie 720 x 480 pixels for NTSC or 720 x 576 pixels for PAL and the quality will be poor with the likelihood they may be blurred and/or pixellated.
First, I do have to ask: what happened to the missing photos? Have you deleted them? It's always a very difficult decision as to what to retain and what to discard on a computer, in order to release disc space, but for as far back as I can remember, the answer has always been to maintain backup copies of files, stored somewhere away from the computer, perhaps on a hard disc that is connected to the computer only when you need to retrieve an old file or add further files to your backup. Or use a Cloud service.
Theoretically, it should be possible to do this but the process is not at all easy because first, you will need to extract the individual .vob files from the source DVD. There is downloadable software that will enable you to do this but you need to be aware that manufacturers of commercial DVDs consider such software to be encouraging piracy and so tend to "pressure" manufacturers/suppliers of such software to not make it easily available. OTOH, if you still have the folder of files which PS created before it actually burned the disc, look inside that folder and you should see one or several .vob files. It is those files you need.
Place any one of them on the Timeline view in PS, position the cursor on the first of the images and go to File>Export>Single frame as ... and select whichever format of the exported image you wish to use, .jpg, .bmp or .png. Choose to save the image to somewhere where it will not be deleted from your computer!!! Repeat the process for every other image and .vob file.
One thing to consider: because the original image may well have been physically quite large, both in dimensions (image size) and number of pixels (resolution), the process of creating the DVD is highly likely to have reduced both the size and resolution and there is no way, without using suitable image enlarging and enhancing software, to regain that original size and resolution.
I'd be very interested to hear how you get on if you decided to try this process. As I wrote earlier, everything in this post is theoretical.