private double xp;
private double yp;
public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
xp = (this.label1.Location.X - this.pictureBox1.Location.X) / Convert.ToDouble(this.pictureBox1.Size.Width);
yp = (this.label1.Location.Y - this.pictureBox1.Location.Y) / Convert.ToDouble(this.pictureBox1.Size.Height);
}

private void pictureBox1_SizeChanged(object sender, EventArgs e)
{
int x = Convert.ToInt32(this.pictureBox1.Size.Width * xp + this.pictureBox1.Location.X);
int y = Convert.ToInt32(this.pictureBox1.Size.Height * yp + this.pictureBox1.Location.Y);
this.label1.Location = new Point(x, y);
}

都放到Panel1里
然后用Scale方法
Panel1.Scale(0.5F);