SignatureWidget -> base64 created with which modification ?

Hello, I'm trying to integrate a signature drawner in my website to save the design of the signature and use it to sign with eSignLive. But the string base64 assign to handdrawn field in the package settings doesn't working if the string is not created by your own signature widget. So my question is: Which modification do you do to base64 string created with JSignature to work well with eSignLive? Because when i retrieve a base64 svg (or another base64) with demo of JSignature on their website, it doesn't work either. So, there is well a process in your own code to transform the base64 string, but which? I have noticed that your base64 string begin always with "AQAAA...". Godinas Maxime.