Create a new page with name DisplayFile.aspx with following code in page load
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Response.ContentType = "image/png";
Response.WriteFile(Server.MapPath("~/images/" + Request.QueryString["file"]));
Response.Flush();
Response.End();
}
}
Now in your actual page where you have IFRAME do this way
<iframe src = "DisplayFile.aspx?file=Chrysanthemum.jpg" height = "200px" width = "200px"></iframe>
<iframe src = "DisplayFile.aspx?file=Jellyfish.jpg" height = "200px" width = "200px"></iframe>
This works in IE, Chrome and FireFox