How to programmatically fill or create filer.fields.image.FilerImageField?

I have some model class with a filer.fields.image.FilerImageField as a field.

from filer.fields.image import FilerImageField
class ModelName(Model):
    icon = FilerImageField(null=True, blank=True)

How to programmatically create or fill an icon field if I have a local path to an image file?