Hi George616,

Referring the below article i have created the example.

Display Binary Image from database in ASP.Net GridView control using C# and VB.Net

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

HTML

<asp:GridView ID="GridView1" runat="server" OnRowDataBound="OnRowDataBound" class="table table-bordered table-condensed table-hover" Width="100%">
    <EmptyDataTemplate>
        <div style="text-align: center; font-weight: bolder; font-size: medium;">
            <asp:Label ID="labelTemp" runat="server" Text="No Activity Recorded"></asp:Label>
        </div>
    </EmptyDataTemplate>
    <Columns>
        <asp:TemplateField HeaderText="Image">
            <ItemTemplate>
                <asp:Image ID="Image1" runat="server" Width="30px" Height="30px" />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<div id="dialog" style="display: none">
</div>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/themes/start/jquery-ui.css" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/jquery-ui.min.js"></script>
<script type="text/javascript">
    $(function () {
        $("#dialog").dialog({
            autoOpen: false,
            modal: true,
            height: 400,
            width: 410,
            title: "Zoomed Image"
        });
        $("[id*=GridView1] img").on('mouseenter', function () {
            $('#dialog').html('');
            $('#dialog').append($(this).clone());
            $('#dialog').find('img')[0].style.width = '375px';
            $('#dialog').find('img')[0].style.height = '350px';
            $('#dialog').dialog('open');
        });
    });
</script>

Namespaces

C#

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

VB.Net

Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection conn = new SqlConnection(constr))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter("SELECT Name,Data FROM tblFiles", conn))
            {
                DataTable dt = new DataTable();
                sda.Fill(dt);
                dt.Rows.Add();
                GridView1.DataSource = dt;
                GridView1.DataBind();
            }
        }
    }
}

protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DataRowView dr = (DataRowView)e.Row.DataItem;
        if (dr.Row.Table.Columns.Contains("Data"))
        {
            if (dr["Data"] != DBNull.Value)
            {
                string imageUrl = "data:image/jpg;base64," + Convert.ToBase64String((byte[])dr["Data"]);
                (e.Row.FindControl("Image1") as Image).ImageUrl = imageUrl;
            }
        }
    }
}

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 conn As SqlConnection = New SqlConnection(constr)
            Using sda As SqlDataAdapter = New SqlDataAdapter("SELECT Name,Data FROM tblFiles", conn)
                Dim dt As DataTable = New DataTable()
                sda.Fill(dt)
                dt.Rows.Add()
                GridView1.DataSource = dt
                GridView1.DataBind()
            End Using
        End Using
    End If
End Sub

Protected Sub OnRowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
    If e.Row.RowType = DataControlRowType.DataRow Then
        Dim dr As DataRowView = CType(e.Row.DataItem, DataRowView)
        If dr.Row.Table.Columns.Contains("Data") Then
            If Not IsDBNull(dr("Data")) Then
                Dim imageUrl As String = "data:image/jpg;base64," & Convert.ToBase64String(CType(dr("Data"), Byte()))
                TryCast(e.Row.FindControl("Image1"), Image).ImageUrl = imageUrl
            End If
        End If
    End If
End Sub

Screenshot