If I use the following code without runat=\"server\" the input\'s src works fine and I see the image coming through.
if jQuery is an option than you could try this:
...
Update: Another option is to create a HttpHandler with processing like this
public void ProcessRequest(HttpContext context)
{
var testButtonImageUrl = "https://fpdbs.paypal.com/dynamicimageweb?cmd=_dynamic-image";
context.Response.Redirect(testButtonImageUrl);
}
add in web.config path to handle image.img or whatever and update aspx