In the ye olden demoscene days, we called that "precalc".

Just calculate all the effects up front and then draw them "in real time" :)

If it were "lot of prep" - e.g. a manually-tagged and fixed database of about 100,000 images of people pointing (assuming 100 columns and 100 rows in the browser-viewport) then that's still small enough for an instantaneous response from the web-server, so the relative long busy-time suggests that _something_ computationally expensive is running in the background - such as a "this-pointing-finger-does-not-exist"-engine.

It could just be fake busy. Timing is everything in comedy, so give a first time user a little suspense to think advanced computer magic is happening before the punchline arrives.

Exactly. Looking at the JS code (even minified), you can see that it's calling a setTimeout for effect - possibly also waiting for image load-, but all the data is there already.

If it runs instantaneously, it would probably be a pretty cool effect to have the pointing fingers trace your cursor as it moves.

If I had a piece of ML that could do that, I'd just run it once on the server and grab a coffee as it generates a set of 100k labeled images for me.

IIRC, the "this X does not exist" sites also don't run ML on request, but serve cached images. At least that was my impression from getting the same image more than once when I spammed F5 fast enough.