'Load the image part collection with all the image parts in package.'

def _gather_image_parts(self):

    for rel in self.iter_rels():
        if rel.is_external:
            continue
        if (rel.reltype != RT.IMAGE):
            continue
        if (rel.target_part in self.image_parts):
            continue
        self.image_parts.append(rel.target_part)
