How to display binary images into a gridview in ASP.NET using C#?

You can use handler to display image in gridview , your html markup look like inside

Gridview ItemTemplate set image control src as src=~/ShowImage.ashx?id=" + id

where ShowImage.ashx is your handler which return MemoryStream((byte[])img);

In your case your querystring is characterID

so your image src would be src=~/ShowImage.ashx?id=" + characterID

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Updated Answer:

Html Markup:

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:TemplateField HeaderText="CharacterID">
            <ItemTemplate>
                <asp:Label ID="lblid" runat="server" Text="<%# Bind("characterID") %>"></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="GameLevel">
            <ItemTemplate>
                <asp:Label ID="lblglevel" runat="server" Text="<%# Bind("gameLevel") %>"></asp:Label>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Image">
            <ItemTemplate>
                <asp:Image ID="Image1" runat="server" ImageUrl="<%#"ShowImage.ashx?getID="+Eval("characterID") %>" />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Code behind:

protected void Page_Load(object sender, EventArgs e)
{        
    DataTable dt = getData();
    GridView1.DataSource = dt;
    GridView1.DataBind();
  }

public  DataTable getData() 
{
  SqlDataAdapter dap = new SqlDataAdapter("select characterID,blueBallImage,gameLevel from CorrespondingBall", cn);
  DataSet ds = new DataSet();
  dap.Fill(ds);
  return ds.Tables[0];
}

Generic handler: Add new generic handler here showIamges.ashx is my generic handler

public void ProcessRequest(HttpContext context)
 {
    Int32 my_Id;
    if (context.Request.QueryString["getID"] != null)
    {
       my_Id = Convert.ToInt32(context.Request.QueryString["getID"]);
       context.Response.ContentType = "image/jpeg";
       Stream strm = ShowEmpImage(my_Id);
       byte[] buffer = new byte[4096];
       int byteSeq = strm.Read(buffer, 0, 4096);
       while (byteSeq > 0)
        {
           context.Response.OutputStream.Write(buffer, 0, byteSeq);
           byteSeq = strm.Read(buffer, 0, 4096);
        }
      }
}

public Stream ShowEmpImage(int my_Id)
{
   string conn = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
   SqlConnection connection = new SqlConnection(conn);
   string sql = "select blueBallImage from CorrespondingBall WHERE characterID = @ID";
   SqlCommand cmd = new SqlCommand(sql, connection);
   cmd.CommandType = CommandType.Text;
   cmd.Parameters.AddWithValue("@ID", my_Id);
   connection.Open();
   object img = cmd.ExecuteScalar();
   return new MemoryStream((byte[])img);
 }