private void button1_Click(object sender, EventArgs e)
        {
            if (button1.BackgroundImage==Properties.Resources.start)
            {
                button1.BackgroundImage = Properties.Resources.stop;
            }
            else
            {
                button1.BackgroundImage=Properties.Resources.start;
            }
        }

以上是不完全成功代码

private void button1_Click(object sender, EventArgs e)
        {
            if (isStart==false)
            {
                button1.BackgroundImage = Properties.Resources.stop;
                isStart = true;
            }
            else
            {
                button1.BackgroundImage = Properties.Resources.start;
                isStart = false;
            }
        }