Screencaping Question

I hope it's O.K to ask this here, as it relates to making icons even if its not specifically about an icon.

I was wondering if anyone knows how to screencap bluray movies like you can with DVDs in KMPlayer/VLC Media player etc.  I have looked everywhere but can't find anything, but have saw people posting bluray screencaps before.  The reason I am asking if that I want to screencap a few bluray movies I have in order to make icons/walls etc. out of them and even share the caps.

Thanks in advance