Recently isn't strange to see films in DVD format (unchanged or edited).
As far as I know, most of the screencapture programs aren't able to make captures of the whole film, so most users makes captures of each VOB file of the film (so if the film has 5 VOB files, they make 5 jpg files).
Media Player Classic (MPC) can make a screencapture of the whole film, but not if you open the DVD or the whole VIDEO_TS folder.
To make a screencapture of the full DVD film open its VTS IFO file with Media Player Classic and then go to File->Save Thumbnails -> specify the settings that appear in the screen. Usually the VTS IFO file of the main features correspond to the biggest VTS VOB file. This trick works in most DVD titles, depending of the structure of the DVD.
At the end you will have a file like the following.
Caps->
<-caps.
Notice that appears the name and the size of the IFO file and the caps of the whole film with the resolution and length of the full film, nevertheless in some cases the length isn't accurate (ie: multiangle) and is better to put the details obtained by other methods (ie: playing the film).