Quote from:-
https://www.arduino.cc/en/Guide/MKR1000
The microcontroller on the MKR1000 runs at 3.3V, which means that you must never apply more than 3.3V to its Digital and Analog pins. Care must be taken when connecting sensors and actuators to assure that this limit of 3.3V is never exceeded. Connecting higher voltage signals, like the 5V commonly used with the other Arduino boards, will damage the MKR1000.
So that means the signal output will also be 3V3 which is not enough to reliably drive a WS2812 powered at 5V.
You need something to boost the signal to 5V, I normally use something like this:-
I do this for using the 3V3 raspberry Pi but it will also work for the MKR1000.
By the way you can find out how to post images here by reading
How to use this forum
And
image guide