Hello 
carlywight,
I see what you're problem ^^'
Probably a setting in my code I will change
Trying differents things and edit my post, stay connected
EDIT :
Yay !
Solution found !
No need to redownload plugin (no changes to code)
Do exactly same like that :
In summarry : You just avec to put in base64 field : tokenat(canvassnapshot, 1, ",")
Why ?
Because canvas snapshot retun string in format : "data:image/png;base64,xxxxxxxxxxx"
So parse snapshot uri string with "tokenat" and return result with index 1 and "," as separator : it return only base64 string and you can use it !