Hi nauna,

Check this example. Now please take its reference and correct your code.

Database

I have made use of the following table tblFiles with the schema as follows.

I have inserted few records in the table. You can refer below article for insert binary data.

Display images from SQL Server Database in ASP.Net GridView control

You can download the database table SQL by clicking the download link below.

Download SQL file

HTML

<div align="center">
    <asp:ListView ID="ListView1" runat="server">
        <ItemTemplate>
            <asp:Label ID="Label1" runat="server" Text='<%#Eval("category_id") %>'></asp:Label>
            <asp:LinkButton ID="LinkButton1" runat="server">View Detail</asp:LinkButton>
        </ItemTemplate>
    </asp:ListView>
    <div id="MyPopup" class="modal fade" role="dialog">
        <div class="modal-dialog">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal">
                        &times;</button>
                    <h4 class="modal-title text-center">
                        Category Details
                    </h4>
                </div>
                <div class="modal-body text-center">
                    <asp:Label ID="lblName" runat="server" Font-Bold="true" />
                    <hr />
                    <asp:Image ID="imgCategory" runat="server" />
                </div>
                <div class="modal-footer">
                    <input type="button" id="btnClosePopup" value="Close" class="btn btn-danger" data-dismiss="modal" />
                </div>
            </div>
        </div>
    </div>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css" />
    <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
    <script type="text/javascript" src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
    <script type="text/javascript">
        $(function () {
            $('[id*=LinkButton1]').on('click', function () {
                $('#MyPopup').find('[id*=lblName]').html('');
                $('#MyPopup').find('[id*=imgCategory]').attr('src', '');
                var categoryId = $(this).prev('[id*=Label1]').html();
                $.ajax({
                    type: "POST",
                    url: "Default.aspx/GetDetails",
                    data: '{id: ' + categoryId + ' }',
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: function (response) {
                        $('#MyPopup').find('[id*=lblName]').html(response.d[1]);
                        $('#MyPopup').find('[id*=imgCategory]').attr('src', response.d[0]);
                        $('#MyPopup').modal('show');
                    },
                    error: function (response) { alert(response.responseText); }
                });
                return false;
            });
        });
    </script>
</div>

Namespaces

C#

using System.Configuration;
using System.Data.SqlClient;
using System.Web.Services;

VB.Net

Imports System.Configuration
Imports System.Data.SqlClient
Imports System.Web.Services

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        System.Data.DataTable dt = new System.Data.DataTable();
        dt.Columns.Add(new System.Data.DataColumn("category_id"));
        dt.Rows.Add(1);
        dt.Rows.Add(2);
        dt.Rows.Add(3);
        ListView1.DataSource = dt;
        ListView1.DataBind();
    }
}

[WebMethod]
public static object[] GetDetails(int id)
{
    object[] details = null;
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT Name,Data FROM tblFiles WHERE Id = @Id"))
        {
            cmd.Parameters.AddWithValue("@Id", id);
            cmd.Connection = con;
            con.Open();
            SqlDataReader sdr = cmd.ExecuteReader();
            if (sdr.Read())
            {
                byte[] bytes = (byte[])sdr["Data"];
                string base64String = Convert.ToBase64String(bytes, 0, bytes.Length);
                string imageUrl = "data:image/png;base64," + base64String;
                string name = sdr["Name"].ToString();
                details = new object[] { imageUrl, name };
            }
            con.Close();
        }
    }

    return details;
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As System.Data.DataTable = New System.Data.DataTable()
        dt.Columns.Add(New System.Data.DataColumn("category_id"))
        dt.Rows.Add(1)
        dt.Rows.Add(2)
        dt.Rows.Add(3)
        ListView1.DataSource = dt
        ListView1.DataBind()
    End If
End Sub

<WebMethod()>
Public Shared Function GetDetails(ByVal id As Integer) As Object()
    Dim details As Object() = Nothing
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand("SELECT Name,Data FROM tblFiles WHERE Id = @Id")
            cmd.Parameters.AddWithValue("@Id", id)
            cmd.Connection = con
            con.Open()
            Dim sdr As SqlDataReader = cmd.ExecuteReader()
            If sdr.Read() Then
                Dim bytes As Byte() = CType(sdr("Data"), Byte())
                Dim base64String As String = Convert.ToBase64String(bytes, 0, bytes.Length)
                Dim imageUrl As String = "data:image/png;base64," & base64String
                Dim name As String = sdr("Name").ToString()
                details = New Object() {imageUrl, name}
            End If
            con.Close()
        End Using
    End Using

    Return details
End Function

Screenshot