The last one is a girl holding the Pokemon Ditto. It changes shaped to look like the opponent it fights, so the joke is that it can be anything, but she likes it as it is (a purple blob).
If you know Pokemon, it kinda is as it plays around with a good saying.
However, like all American humour, if you don't watch the show or play the game, you're going to be lost.
It's not an inside joke it very much is pop culture. These are phenomenons that are international in nature, I'm sure if I put that in other languages you'd have them in stitches too. Also how can you surmise it to just a country when it is tons of countries I play the game(pokemon) still even in my 20s and when you go to their international site, you can see millions playing around the world and avid as well, they'd probably laugh at the reference that was just posted. I mean doge was already kicked out of here, do people really need to complain about other types that are more engaging and vast? I got the Shark one you posted but I thought it was lame. As for @Jimlaad43 I agreed with much of what you said, but Colbert is flippin hilarious.
Maybe it's me being good a trivia and watching tons of stuff or retaining useless info, but even the Star Trek stuff you posted I found funny. Just like the Radcliffe picture was funny because of the pop culture on two parts it played on him being the live version of Harry Potter and looking drugged out.
That just seems really disturbing to me.
