TestButton

gistfile1.txt

using UnityEngine;
using System.Collections;

public class TestButton : MonoBehaviour {
    [SerializeField] string imageUrl;
    UITexture texture;

    void Awake()
    {
        texture = GetComponent<UITexture>();
    }

    IEnumerator Start()
    {
        WWW www = new WWW(imageUrl);
        yield return www;
        texture.mainTexture = www.texture;
    }
}