Argument exception was unhandled , path is not in legal form

If the user selects "OK", you're storing the selected path in textBox1. You're then trying to open the file based on the value of textBox4, which almost certainly doesn't contain a valid file path.

If the user selects "Cancel", you're still trying to open the file based on the value of textBox4.

Change your code to use the correct path, and only process the path if the user selects "OK":

private void button1_Click(object sender, EventArgs e)
{
    using (OpenFileDialog open = new OpenFileDialog())
    {
        open.Filter = "Image Files(*.jpeg;*.bmp;*.png;*.jpg)|*.jpeg;*.bmp;*.png;*.jpg";
        if (open.ShowDialog() == DialogResult.OK)
        {
            textBox1.Text = open.FileName;
            
            // TODO: Do something with these...
            Bitmap bitmap = new Bitmap(open.FileName);
            byte[] bimage = File.ReadAllBytes(open.FileName);
        }
    }
}

Also, do yourself a favour and give your controls meaningful names. You might remember that textBox1 is the image path and textBox42 is the frood-name now, but when you come back to your code in a few weeks' time, you'll have forgotten what these controls represent.

THIS WORKED FINE AS PER MY NEEDS. POSTING IT SO OTHERS MIGHT GET HELP
private void button1_Click(object sender, EventArgs e)
{
openFileDialog1.Filter = "jpg files (*.jpg)|*.jpg|All files (*.*)|*.*";


OpenFileDialog openImage = new OpenFileDialog();
DialogResult result = openImage.ShowDialog();
if (result == DialogResult.OK)
{
//Load image in picture box and set size mode property of image as normal.
pictureBox1.Load(openImage.FileName);
pictureBox1.SizeMode = PictureBoxSizeMode.AutoSize;
//Store source location of image in textbox.
textBox1.Text = openImage.FileName;
//Retrive height and width of image and store in OriginalImageSize variable.
int imgWidth = pictureBox1.Image.Width;
int imgHeight = pictureBox1.Image.Height;
OriginalImageSize = new Size(imgWidth, imgHeight);
string imgSize = "Width " + imgWidth + " px Height " + imgHeight + " px";

//image width greater than 102 or height greater than 76then only Resize
if (pictureBox1.Image.Width > 102 || pictureBox1.Image.Height > 76)
{
Image scaledImage = ScaleByPercent(pictureBox1.Image, 10);
pictureBox1.Image = scaledImage; //Display that image in picture box.
//Retrive width and height of image.
imgSize = "Width " + scaledImage.Width + " px Height " + scaledImage.Height + " px";
pictureBox1.Image.Save("@path", ImageFormat.Jpeg);
}
else
{
imgSize = "Width " + pictureBox1.Image.Width + " px Height " + pictureBox1.Image.Height + " px";
}
pictureBox1.Image.Save("@path",ImageFormat.Jpeg);

}


}