public partial class Form1 : Form
    {
        int imageNumber = 0;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer1.Start();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer1.Stop();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            if (imageNumber == imageList1.Images.Count - 1)
            {
                imageNumber = 0;
            }
            imageNumber++;

            pictureBox1.Image = imageList1.Images[imageNumber];

            textBox1.Text = imageNumber.ToString();
        }
    }
}