That's a pretty funny parody of BBC Test Card F: https://en.wikipedia.org/wiki/Test_Card_F

I remember at school the TV was wheeled in and the class was told we were going to watch something. Whatever the programme was, it wasn't on and we got the test card. The headmaster popped his head in and told us all to watch it carefully as the girl will draw on the board at the end.

We all watched it for what felt like hours. Strangest day ever.

Yep that's the one. It was done by Noel Fielding and Julian Barratt under the guise of The Mighty Boosh.

Which you may recognize as the show behind Old Gregg

At least here in the US, Old Gregg is pretty well known outside of The Mighty Boosh. It went around independently as a viral video a few years ago and wasn't directly associated with The Mighty Boosh.

I'm in the US, and that's why I mentioned it... because it's so popular on its own, not many people realize it's from the Mighty Boosh or any show for that matter.

For some reason, I was unable to reply to petercooper's comment earlier. This was meant for him.

A "few"... it's almost 10 years old.

Please don't remind me of the quick and inevitable passing of time towards nothingness. That's a disrespectful thing to do on a Friday morning.

Is Old Gregg otherwise famous separate from the show?

In the US, most people just know the viral video of it and don't realize it's actually from a show

A well communicative dummy image.

At a former job, our standard test image was the jellollama GIF.