Hey abualmazen,

Please refer below sample, And for modal popup refer below link.

Open (Show) Bootstrap Modal Popup Window on Page Load in ASP.Net

HTML

C#

<asp:DataList runat="server" ID="dlCustomers" RepeatDirection="Horizontal">
    <ItemTemplate>
        <asp:Button Text='<%#Eval("Name") %>' runat="server" ID="btnid" OnClick="save" />
        <asp:HiddenField Value='<%#Eval("CustomerId") %>' runat="server" ID="hfid" />
    </ItemTemplate>
</asp:DataList>
<br />
<asp:DataList runat="server" ID="dlButtons" RepeatDirection="Horizontal">
    <ItemTemplate>
        <asp:HiddenField Value='<%#Eval("id") %>' runat="server" ID="hfid1" />
        <asp:ImageButton ID="img" ImageUrl='<%# "data:image/jpg;base64," + Convert.ToBase64String((byte[])Eval("Data")) %>'
            runat="server" OnClick="getOnImageClick" />
    </ItemTemplate>
</asp:DataList>
<asp:TextBox ID="txtCustomerId" runat="server" Visible="false" />
<asp:TextBox ID="txtName" runat="server" Visible="false" />
<asp:HiddenField ID="hf" runat="server" />

VB.Net

<asp:DataList runat="server" ID="dlCustomers" RepeatDirection="Horizontal">
    <ItemTemplate>
        <asp:Button Text='<%#Eval("Name") %>' runat="server" ID="btnid" OnClick="save" />
        <asp:HiddenField Value='<%#Eval("CustomerId") %>' runat="server" ID="hfid" />
    </ItemTemplate>
</asp:DataList>
<br />
<asp:DataList runat="server" ID="dlButtons" RepeatDirection="Horizontal">
    <ItemTemplate>
        <asp:HiddenField Value='<%#Eval("id") %>' runat="server" ID="hfid1" />
        <asp:ImageButton ID="img" ImageUrl='<%# "data:image/jpg;base64," + Convert.ToBase64String(CType(Eval("Data"), Byte())) %>'
            runat="server" OnClick="getOnImageClick" />
    </ItemTemplate>
</asp:DataList>
<asp:TextBox ID="txtCustomerId" runat="server" Visible="false" />
<asp:TextBox ID="txtName" runat="server" Visible="false" />
<asp:HiddenField ID="hf" runat="server" />

Namespaces

C#

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

VB.Net

Imports System.Data.SqlClient
Imports System.Data

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT CustomerId, Name From Customers", con))
            {
                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    DataTable dt = new DataTable();
                    da.Fill(dt);
                    this.dlCustomers.DataSource = dt;
                    this.dlCustomers.DataBind();
                }
            }
        }
    }
}

protected void save(object sender, EventArgs e)
{
    Button btn = (sender) as Button;
    DataListItem item = (DataListItem)btn.NamingContainer;
    string id = ((HiddenField)item.FindControl("hfid")).Value;
    DataTable dt = GetData(id);
    DataTable dt1 = new DataTable();
    dt1.Columns.Add("id");
    dt1.Columns.Add("Data", typeof(byte[]));
    ImageButton img = (ImageButton)item.FindControl("img");
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        dt1.Rows.Add(dt.Rows[i]["id"], dt.Rows[i]["Data"]);
    }
    dlButtons.DataSource = dt1;
    dlButtons.DataBind();
}

private DataTable GetData(string id)
{
    string constr = ConfigurationManager.ConnectionStrings["constr1"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT id, Name,Data From tblFiles WHERE id = @Id", con))
        {
            cmd.Parameters.AddWithValue("@Id", id);
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                DataTable dt = new DataTable();
                da.Fill(dt);
                return dt;
            }
        }
    }
}

protected void getOnImageClick(object sender, ImageClickEventArgs e)
{
    txtCustomerId.Visible = true;
    txtName.Visible = true;
    ImageButton imgbtn = (sender) as ImageButton;
    DataListItem item = (DataListItem)imgbtn.NamingContainer;
    string id = ((HiddenField)item.FindControl("hfid1")).Value;
    DataTable dt = GetData(id);
    txtCustomerId.Text = id.ToString();
    txtName.Text = dt.Rows[0]["Name"].ToString();
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using con As SqlConnection = New SqlConnection(constr)
            Using cmd As SqlCommand = New SqlCommand("SELECT CustomerId, Name From Customers", con)
                Using da As SqlDataAdapter = New SqlDataAdapter(cmd)
                    Dim dt As DataTable = New DataTable()
                    da.Fill(dt)
                    Me.dlCustomers.DataSource = dt
                    Me.dlCustomers.DataBind()
                End Using
            End Using
        End Using
    End If
End Sub

Protected Sub save(ByVal sender As Object, ByVal e As EventArgs)
    Dim btn As Button = TryCast((sender), Button)
    Dim item As DataListItem = CType(btn.NamingContainer, DataListItem)
    Dim id As String = (CType(item.FindControl("hfid"), HiddenField)).Value
    Dim dt As DataTable = GetData(id)
    Dim dt1 As DataTable = New DataTable()
    dt1.Columns.Add("id")
    dt1.Columns.Add("Data", GetType(Byte()))
    Dim img As ImageButton = CType(item.FindControl("img"), ImageButton)

    For i As Integer = 0 To dt.Rows.Count - 1
        dt1.Rows.Add(dt.Rows(i)("id"), dt.Rows(i)("Data"))
    Next

    dlButtons.DataSource = dt1
    dlButtons.DataBind()
End Sub

Private Function GetData(ByVal id As String) As DataTable
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr1").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand("SELECT id, Name,Data From tblFiles WHERE id = @Id", con)
            cmd.Parameters.AddWithValue("@Id", id)

            Using da As SqlDataAdapter = New SqlDataAdapter(cmd)
                Dim dt As DataTable = New DataTable()
                da.Fill(dt)
                Return dt
            End Using
        End Using
    End Using
End Function

Protected Sub getOnImageClick(ByVal sender As Object, ByVal e As ImageClickEventArgs)
    txtCustomerId.Visible = True
    txtName.Visible = True
    Dim imgbtn As ImageButton = TryCast((sender), ImageButton)
    Dim item As DataListItem = CType(imgbtn.NamingContainer, DataListItem)
    Dim id As String = (CType(item.FindControl("hfid1"), HiddenField)).Value
    Dim dt As DataTable = GetData(id)
    txtCustomerId.Text = id.ToString()
    txtName.Text = dt.Rows(0)("Name").ToString()
End Sub

Screenshot