The image to edit. Must be a valid PNG file, less than 4MB,
and square. If mask is not provided, image must have transparency,
which will be used as the mask.image
file name is image
An additional image whose fully transparent areas
(e.g. where alpha is zero) indicate where should be edited.
Must be a valid PNG file, less than 4MB, and have
the same dimensions as image. mask
file name is mask