ASP.NET

string imageid = context.Request.QueryString["UserID"];
...
new SqlCommand("select UserID,Image FROM Users where UserID=" + imageid, connection);

public sealed class Handler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        string imageid = context.Request.QueryString["UserID"];
        string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;

        // Use "using" blocks to clean up automatically:
        using (SqlConnection connection = new SqlConnection(connectionString))
        using (SqlCommand command = new SqlCommand("SELECT UserID, Image FROM Users WHERE UserID = @UserID", connection))
        {
            // Use a parameterized query to avoid SQL injection:
            command.Parameters.AddWithValue("@UserID", imageid);

            connection.Open();
            using (SqlDataReader dr = command.ExecuteReader(CommandBehavior.CloseConnection))
            {
                // The image might not exist!
                if (!dr.Read()) throw new HttpException(404, "Image not found.");

                // Add the correct type here:
                context.Response.ContentType = "image/jpeg";
                context.Response.BinaryWrite((byte[])dr[dr.GetOrdinal("Image")]);
            }
        }
    }

    public bool IsReusable
    {
        get { return true; }
    }
}

<asp:TemplateField HeaderText="Image">
                 <ItemTemplate>
                    <asp:Image ID="Image1" runat="server" ImageUrl='<%#"Handler.ashx?UserID=1;"+Eval("UserID")%>' Height="150px" Width="150px"/>
                 </ItemTemplate>
            </asp:TemplateField>

<Image ID="Image1" runat="server" ImageUrl="Handler.ashx" Height="150px" Width="150px"/>

var cookie = context.Request.Cookies["userid"];
if (null == cookie) throw new HttpException(404, "Cookie not found.");
string imageid = cookie.Value;

<system.web>
      <httpHandlers>
        <add verb="*" path="Handler.ashx" type="ShowImage,System.Web.UI.SimpleHandlerFactory" validate="true" />
      </httpHandlers>

      <urlMappings enabled="true">
        <add url="~/MyProfile.aspx" mappedUrl="~/Handler.ashx"/>
      </urlMappings>
</system.web>

public void ProcessRequest(HttpContext context)
        {

            var cookie = context.Request.Cookies["userid"].Values.ToString();
            if (null == cookie) throw new HttpException(404, "Cookie not found.");
            string imageid = cookie;
         //   string imageid = context.Request.QueryString["UserID"];
            string connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;


            // Use "using" blocks to clean up automatically:
            using (SqlConnection connection = new SqlConnection(connectionString))
            using (SqlCommand command = new SqlCommand("SELECT UserID, Image FROM Users WHERE UserID = @userID", connection))
            {
                // Use a parameterized query to avoid SQL injection:
                command.Parameters.AddWithValue("@userID", imageid);

                connection.Open();
                using (SqlDataReader dr = command.ExecuteReader(CommandBehavior.CloseConnection))
                {
                    // The image might not exist!
                    if (!dr.Read()) throw new HttpException(404, "Image not found.");

                    // Add the correct type here:
                    context.Response.ContentType = "image/jpeg";
                   // context.Response.BinaryWrite((byte[])dr[dr.GetOrdinal("Image")]);
                    context.Response.BinaryWrite((byte[])dr["Image"]);
                }
            }

        }

var cookie = context.Request.Cookies["userid"];
if (null == cookie) throw new HttpException(404, "Cookie not found.");
string imageid = cookie.Value;

navigating directly to the handler