It’s funny how Tumblr is shitting its pants over the fact that The Dover Boys is in the public domain. Buddy, it doesn’t matter; even if anyone cared enough to try and stop you, all your remixes and memes are already covered under fair use. Unless you’re compiling material for a quick cash grab 1001 PUBLIC DOMAIN CARTOONS DVD to sell in the dollar store check-out lane, this makes no difference to you.
Don’t be jealous just ‘cause I’m makin’ that cheddar, son.
They’re covered under fair use assuming you have time and money to defend that.