jquery alert on file upload for image

A simple file upload

    <dl>
     <dt><label for="fileupload">{L_FILENAME}:</label></dt>
      <dd>
        <input type="file" name="fileupload" id="fileupload" maxlength="{FILESIZE}" value="" /> 
     </dd>
    </dl>

need a check for images (jpg, jpeg, gif, png). When there is a image, a alert message should say: "You are try to upload a image. Please use the image uploader".

Note: The image-check should start direct after the file is selected and not when submited the form. Is this possible with jquery?

I tried many solutions without success. Thank you!