您可以有你的通用处理程序返回404状态code如果图像不存在：

 公共无效的ProcessRequest（HttpContext的背景下）
{
    字符串ID = context.Request.QueryString [ID];
    字符串构造= System.Configuration.ConfigurationManager.ConnectionStrings [EmployeeDatabase]的ConnectionString。
    使用（VAR CON =新的SqlConnection（构造））
    使用（VAR CMD = con.CreateCommand（））
    {
        con.Open（）;
        cmd.CommandText =的getImage;
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue（@的EmpID，身份证）;
        使用（VAR博士= cmd.ExecuteReader（））
        {
            如果（dr.Read（））
            {
                //图像被发现
                字节[] = imageBytes（字节[]）dr.GetValue（0）;
                //不要忘记设置正确的内容类型
                context.Response.ContentType =图像/ PNG
                context.Response.BinaryWrite（imageBytes）;
            }
            其他
            {
                //没有在数据库= GT找到的记录;返回404
                context.Response.Status code = 404;
            }
        }
    }
}
 

和然后在客户端上可以使用一个Web客户端来测试，如果图像中存在

  VAR图片网址=〜/ Handler2.ashx n =？+ EMPID;
VAR基本URI =新的URI（Request.Url.GetLeftPart（UriPartial.Authority））;
VAR URL =新的URI（基本URI，VirtualPathUtility.ToAbsolute（图片网址））;
使用（VAR的客户=新的HttpClient（））
{
    VAR要求=新的Htt prequestMessage（HttpMethod.Head，URL）;
    VAR响应= client.SendAsync（要求）。结果;
    如果（response.IsSuccessStatus code）
    {
        //图像存在：
        PageLinkBut​​ton.Text =更新形象;
        Image2.ImageUrl =图片网址;
    }
    其他
    {
        //图像不存在：
        PageLinkBut​​ton.Text =添加映像;
    }
}
 

Handler

public class Handler2 : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        string id = context.Request.QueryString["Id"];
        string constr = System.Configuration.ConfigurationManager
            .ConnectionStrings["EmployeeDatabase"].ConnectionString;
        SqlConnection con = new SqlConnection(constr);

        con.Open();
        SqlCommand cmd = new SqlCommand("GetImage", con);
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@EmpID", id);
        //cmd.Parameters.AddWithValue("@Gender", ge);
        SqlDataReader dr = cmd.ExecuteReader();
        dr.Read();

        if (dr.HasRows)
        {
            byte[] imageBytes = (byte[])dr.GetValue(0);
            context.Response.BinaryWrite(imageBytes);
        }

        dr.Close();
        con.Close();
    }

User Control

public void BindGridviewData()
{
    String empid1 = Name;
    // String empid1 = Request.QueryString["MyText"];
    int empid = int.Parse(empid1);
    //int empid = 1500422;
    string constr = System.Configuration.ConfigurationManager
        .ConnectionStrings["EmployeeDatabase"].ConnectionString;
    SqlConnection con = new SqlConnection(constr);

    con.Open();
    SqlCommand cmd = new SqlCommand("GetEmployeeDetails", con);
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.Add("@EmpID", SqlDbType.Int, 0).Value = empid;
    SqlDataReader dr = cmd.ExecuteReader();
    dr.Read();

    Label9.Text = dr[0].ToString();
    Label2.Text = dr[1].ToString();
    Label3.Text = dr[2].ToString();
    Label4.Text = dr[3].ToString();
    Label5.Text = dr[4].ToString();
    Label6.Text = dr[5].ToString();
    Label7.Text = dr[6].ToString();
    Label8.Text = dr[7].ToString();

    Image2.ImageUrl = "~/Handler2.ashx?Id=" + empid;
}

In the above program if we are not getting image in image control we need to display the text on button as "Add your Image" and if we have image we need to display it as "Update your Image"

I have used following ways which are not working:

Option 1

 if (Image2.ImageUrl != null)
 {
     PageLinkButton.Text = "Upadte your Image";
 }
 else
 {
     PageLinkButton.Text = "Add your Image";
 } 

Option 2

WebClient client = new WebClient();
byte[] Value = client.DownloadData(Image2.ImageUrl);

if (Value != null)
{
    PageLinkButton.Text = "Update your Image";
}
else
{
    PageLinkButton.Text = "Add your Image";
}  

You could have your generic handler return 404 status code if the image doesn't exist:

public void ProcessRequest(HttpContext context)
{
    string id = context.Request.QueryString["Id"];
    string constr = System.Configuration.ConfigurationManager.ConnectionStrings["EmployeeDatabase"].ConnectionString;
    using (var con = new SqlConnection(constr))
    using (var cmd = con.CreateCommand())
    {
        con.Open();
        cmd.CommandText = "GetImage";
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@EmpID", id);
        using (var dr = cmd.ExecuteReader())
        {
            if (dr.Read())
            {
                // the image was found
                byte[] imageBytes = (byte[])dr.GetValue(0);
                // Don't forget to set the proper content type
                context.Response.ContentType = "image/png";
                context.Response.BinaryWrite(imageBytes);
            }
            else
            {
                // no record found in the database => return 404
                context.Response.StatusCode = 404;
            }
        }
    }
}

and then on the client you could use a WebClient to test if the image exists:

var imageUrl = "~/Handler2.ashx?Id=" + empid;
var baseUri = new Uri(Request.Url.GetLeftPart(UriPartial.Authority));
var url = new Uri(baseUri, VirtualPathUtility.ToAbsolute(imageUrl));
using (var client = new HttpClient())
{
    var request = new HttpRequestMessage(HttpMethod.Head, url);
    var response = client.SendAsync(request).Result;
    if (response.IsSuccessStatusCode)
    {
        // the image exists:
        PageLinkButton.Text = "Update your Image";
        Image2.ImageUrl = imageUrl;
    }
    else
    {
        // the image does not exist:
        PageLinkButton.Text = "Add your Image";
    }
}