As side question from solved question Odoo 10 - Show image of a given product template
Which are the differences between returning this one:
product_image = self.browse(product_id).image
image = product_image and product_image.decode('base64') or None
return tools.image_resize_image_big(image.encode('base64'))
and this:
product_image = self.browse(product_id).image
return product_image
where in both cases self is an instance of product.template
Image is going to be used-displayed in:
<field widget="image" class="oe_avatar"/>