của chế

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            for (int i = 0; i < 5; i++)
            {
                PictureBox pb = new PictureBox();
                pb.Width = 50;
                pb.Height = 50;
                pb.Tag = i;
                pb.BackColor = Color.Red;

                pb.Click += Pb_Click;

                flowLayoutPanel1.Controls.Add(pb);
            }
        }

        private void Pb_Click(object sender, EventArgs e)
        {
            MessageBox.Show((sender as PictureBox).Tag.ToString());
        }
    }