string allowedimages = System.Configuration.ConfigurationManager.AppSettings["allowedimages"];
type = Path.GetExtension(Uploadlogo.PostedFile.FileName);
if (allowedimages.IndexOf(type) == -1)
{
}
else{
}
In web.config file
<appsettings>
<add key="AllowedImages" value=".jpeg,.JPEG,.jpe,.JPE,.jpg,.JPG,.gif,.GIF,.bmp,.BMP,.ico,.ICO"/>
</appsettings>