TIL The number of the beast is 5000, horns in the air people!.

Is it just me, or are several of the hand gestures presented in that image so alike that it would be completely impossible to tell them apart in practice? The main difference between 10 and 90 or between 100 and 900 seems to be the amount of shadow on your hand, which sounds like an impractical arbiter in finger counting. And six and seven appear to require the counter to actually break their fingers first in order to even be physically possible.

@JanusBahsJacquet No. It's not just you, but it's important at which joint the finger points at?

I wonder if there were any civilisations that used their fingers to count in binary - it is the obvious use of digits...

@DrMcCleod "Digital" is Latin and means…?

@LangLangC: Digital and Dactylo (Greek finger) and Arabic التصاعدي (upward) and orther meanings like اليد تصعد الزيادة coming from the counting of the fingers on the hand.

עלו את היד Raise your hand

@NicHartley Oh, I see. That may well be – that moves the problem one step up the scale, to the abilities of the artist to draw hands facing different ways!

@DrMcCleod, binary four.

@Mark 6 back atcha.

A Roman Centurion walks into a bar. He goes over to the barman and says "Make me a martinus." The barman replies, "Martini; coming right up." The centurion interjects, "Dammit man, if I wanted a double I would've asked for one!"

Looking at some of these pictures literally makes my wrist hurt.

The picture leaves much to be desired. Also, when there are symbols for 4-digit numbers, how would these be shown? A person has only two hands. Using only signs for the ten digits after each other and a separator would be more manageable and intelligible than this chiropractic torture.

@VincenzoOliva The picture shows a different system, however. Showing, say, 1234 requires four symbols here.

@Chieron Oh, I misunderstood your comment. Sure, it would require to make more than two signs, but after all today we may express 20 showing our open palms "twice". At least, in Italy it can happen.

That last edit is a paradox. They "might have used" binary, or duodecimal (base 12), and you have just made all such supposition valid answers, and you question thus off-topic.

@PieterGeerkens The edit you refer to was meant to emphasise that the joke part is really just a joke and opener, as it seemed to me that this part misled you into "prank" territory. Why should the hypothetical binary be off-topic, if it should have been that whioch they used?

Thinking that I saw hat first in another movie than Basterds but apart from the Japanese paper giving out 27 already in the question, there are systems for finger counting around the world looking that are much more difficult than the one I grew up with. I doubt that all these sources were written on April 1st.