private RawImage ddRawImage;
this.ddRawImage = transform.Find("RawImage-dd").GetComponent<RawImage>();

IEnumerator getImage() {
        WWW www = new WWW("http://chicai.group/wp-content/uploads/2017/10/1-6.png");
        yield return www;
        Texture ss = www.texture;
        this.ddRawImage.texture = ss;
}

StartCoroutine(getImage());

通过WWW获取链接上的图片，改变RawImage显示的图片