1) If you KNOW the original source is a bootleg, then yes it is still a bootleg.

2) Why would anyone want to screencap off of a Youtube video. The quality( even at "HD") is still bad compared to a direct cap from a DVD.

3) It gets dicey when you come across stuff that's OLD but unavailable. If you can't buy or rent a video of your favorite old adventure show from the 1950s because the studio went out of business and it was never released anywhere, then I would be more forgiving if it showed up on Youtube and someone capped it. Now new stuff or stuff that is actually available on DVD or LEGAL download for purchase or rent, no bootlegs allowed rule applies.