How to assign an image value from a stream from a text file

I'm trying to implement a feature in a project where the user can upload their own image files to be used as an avatar, I get the stream from the image as jpg format and save it in a text file on the same line with the user's username where it's retrieved but I keep getting the error message "Parameter is not valid" when I try to set the image of a picturebox to the stream, does anyone know what I'm doing wrong?

The code that saves the stream to the text file;

customavatar = Image.FromFile(filename);

var stream = new System.IO.MemoryStream();
customavatar.Save(stream, ImageFormat.Jpeg);
stream.Position = 0;

if(!File.Exists( textfile))
{
    File.Create( textfile);
}
using (StreamWriter sw = File.AppendText( textfile))
{
    sw.WriteLine("");
    sw.WriteLine($"{username},{stream}");
}

The code setting the image of a picturebox to the stream, where the error appears;

string[] filelinesarray = File.ReadAllLines(text file);
foreach (string str in filelinesarray)
{
    if (str.Split(",")[0] == username)
    {
        byte[] byteArray = Encoding.ASCII.GetBytes(str.Split(",")[1]);
        MemoryStream stream = new MemoryStream(byteArray);

        Image img = Image.FromStream(stream);
        picturebox.Image = img;
    }
}

As Fildor said, use base 64 to encode the image.

I tested with winform (.Net Framework4.8) and modified your code.

I customized the save address of a txt file and the name of a username. And use openfiledialog to select the image address that needs to be uploaded.

The following is my demo:

private void button1_Click(object sender, EventArgs e)
{
    var openFileDialog = new OpenFileDialog();
    openFileDialog.Filter = "All Files (*.*)|*.*";
    openFileDialog.Title = "Select a file";
    if (openFileDialog.ShowDialog() == DialogResult.OK)
    {
        string filename = openFileDialog.FileName;
        var stream = new System.IO.MemoryStream();
        using (var customavatar = Image.FromFile(filename))
        {
            customavatar.Save(stream, ImageFormat.Jpeg);
        }
        var base64String = Convert.ToBase64String(stream.ToArray());

        // Create the file, or overwrite if the file exists.
        using (var fstream = new FileStream(textfile, FileMode.Create, FileAccess.Write, FileShare.None))
        {
            using (var writer = new StreamWriter(fstream))
            {
                writer.Write($"{username},{base64String}");
            }
        }
    }
}

private void button2_Click(object sender, EventArgs e)
{
    string[] filelinesarray = File.ReadAllLines(textfile);
    foreach (string str in filelinesarray)
    {
        if (str.Split(',')[0] == username)
        {
            byte[] byteArray = Convert.FromBase64String(str.Split(',')[1]);
            MemoryStream stream = new MemoryStream(byteArray);
            Image img = Image.FromStream(stream);
            pictureBox1.Image = img;
        }
    }
}