Design

<asp:Repeater ID="FileRepeater" runat="server">
    <ItemTemplate>
        <asp:HyperLink ID="HyperLink1" NavigateUrl="" ImageUrl='<%#"Content/Images/" + Eval("Name") %>' runat="server"/> 
    </ItemTemplate>
</asp:Repeater>

Code

using System.IO;

using System.Collections;

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        ListImages();
    }
}

private void ListImages()
{
    DirectoryInfo dir = new DirectoryInfo(Server.MapPath("~"));
    FileInfo[] file = dir.GetFiles();
    ArrayList list = new ArrayList();
    foreach (FileInfo info in file)
    {
        if (info.Extension == ".jpg" || info.Extension == ".jpeg" || info.Extension == ".gif")
        {
            list.Add(info);
        }
    }

    Repeater1.DataSource = list;
    Repeater1.DataBind();
}