[REQ] Auto Grab Image Thumbnails from Youtube

I'm building Vlog (Video Blog) and i embeded all of video from YouTube, but i confuse how to Auto grab the thumbnail from Youtube? Yep, auto grab.
Can anyone help me?

Sorry for my bad english

i dont autograb the screenshots i press the WINDOWS BUTTON and PRNTSCREEN Button on the top left of my keyboard at the same time and it takes a screenshot of my screen. I have PS open so it takes a sec to crop and save.