The relationship between Japanese dogs and Japanese has lasted for a very long time. From ancient time to present, as a hunting dog, a guard dog and a member of family, the relationship has not changed. They have been living with humans, interacting with human life very closely. I will introduce some examples from relic of the past. I can't say for certain, but I guess some dogs that appear in this examples are the near kind of Shiba Inu, which is ancient kind, by judging from their appearance.
Image from " https://ja.wikipedia.org/wiki/%E9%8A%85%E9%90%B8 "
① 袈裟襷文銅鐸(Japanese：Kesadasukimon dotaku, Yayoi period, around 2 B.C. to 1 B.C. )
銅鐸(Japanese：dotaku) is a large musical relic made of copper. The exact usage is unknown, but is presumed to be a ritual utensil. On the surface, there are 12 pictures depicting the living environment of the period. One of them is a picture of a hunter who has a bow and make five dogs surround his game.
Since the dogs have standing ears, it is assumed that they are the ancestors of Japanese dogs. It also shows that hunting has not changed much since 2000 years ago.
Image from "http://www.kurashikikoukokan.com/yomoyama/2013/151.html "
② 十二支彩絵布幕(Japanese：Junishi saieno nunonomaku, Nara period, around 8 A.C.)
十二支(junishi：Japanese zodiac) is a traditional Japanese culture in which 12 different animal names are assigned each year.
12 animals are 子(ne：rat), 丑(ushi：ox), 寅(tora：tiger), 卯(u：rabbit), 辰(tatsu：dragon),巳(mi：snake), 午(uma：horse), 未(hitsuji：sheep), 申(saru：monkey), 酉(tori：rooster), 戌(inu：dog), 亥(i：boar).
In 正倉院(Shoso inn) of 東大寺(Todai ji) temple, the relic of about 1250 years ago still remains, including 650 kinds of treasures and 60 kinds of medicines.
One of them is linen on which Japanese zodiac is drawn.
Unfortunately, about the dog picture, only foot part remains, but the shape and angle of the toes remind me the appearance of Japanese dogs in the Nara period.
③鳥獣人物戯画(Japanese：Tyoju jinbutsu giga, Heian period, around 12 A.C.) 鳥獣(tyoju) means birds and animals. This picture shows playing personified animals. This picture is also said to have been drawn by 鳥羽僧正覚猷(Toba sojo Kakusyu) and be the oldest manga of Japan. In this picture, a white female dog which resembles Shiba Inu, two fighting dogs, and some playing dogs are drawn. In addition, a dog with spots are also drawn, so it proves that there were dogs with spots at that time too.