So I've found out the answer with the help of Clive.
Getting the image URI in Twiga template file is done using
node.field_image.0.entity.uri.value
Getting the full URL for the image can be done using. Provide a Twig extension for file_create_url()
, closed as fixed on January, 2015, made possible to use file_create_urlfile_url(node.field_image.0.entity.uri.value)
Doing this in Twig isn't possible yet but they are working on it -> see herea template file.
{{ file_url(node.field_image.0.entity.uri.value) }}