button lock from Gennadievskaya Bible
 

It's possible image of button lock from Gennadievskaya Bible (Геннадьевская Библия) written in 1499 year in Russia. It's well known fact that button lock was very common in Russia. It's possible that this picture is one of the earliest image of buttonlock

Briliant picture, but i do not see a button mechanism?
It looks like a left handed powderpan with serpentine.

Whow. Do you have a more precise source where this image is from? Unfortunately I only found websites in Kyrillic which is very hard for me to understand.

Also very interesting is the powder horn as there are not many depiction from the 15th century.

Ah I just found the Russian Wikipedia article of the work:
https://ru.wikipedia.org/wiki/%D0%93...BB%D0%B8%D1%8F

and the English article:
https://en.wikipedia.org/wiki/Gennady%27s_Bible

I am not absolutely sure that this lock is a button lock. That is why I've wrote "possibly". But it looks like serpentines on button locks. Maybe I'm wrong

Spiridonov,

The way the gun is being held, and the position of the firing hand, very strongly suggest a snap-lock fired by means of the button on the lock plate.

This May be one of the very earliest depictions of such a lock as you suggest!
I do believe this is the case. Very interesting!!