How do I check if the uploaded file has the right format?
<p>I work with c# and asp.net</p>

<p>I created a webpage with a web form where you enter your information in order to submit it. There is also a file upload on my page: <code>&lt;asp:FileUpload ID="FileUploadPassfoto" runat="server"/&gt;</code> In my c# code behind i coded a IF-Loop which checks if something got uploaded. Like this:</p>

<pre><code>if (FileUploadPassfoto.HasFile == true)
{
      HttpPostedFile file = FileUploadPassfoto.PostedFile;
      using (BinaryReader binaryReader = new BinaryReader(file.InputStream))
      {
          lehrling.passfoto = binaryReader.ReadBytes(file.ContentLength);
      }
      LabelPassfotoError.Visible = false;
}
else
{
     LabelPassfotoError.Visible = true;
     LabelError.Visible = true;
}
</code></pre>

<p>What it does is: As i said it checks if something got uploaded. If nothing got uploaded a ErrorLabel will be shown so the user knows he forgot to upload.</p>

<p>What i want to check too, is if the uploaded file is a image. To be more clear i only want to accept .jpg/.bmp and .gif. If a wrong format gets uploaded i want to display my ErrorLabel as well.</p>

<p>I dont really know how i should do this, can you please help me? Thank you </p>