problema subida banner aleatorio

[maxwellxp]

carga del banner

Código PHP:

<form name='form1' method='post' action='sitio.php' enctype="multipart/form-data">
<table>
<tr>
<td colspan='2'><div align="left">Banner 1</div></td>
</tr>
 
<tr>
<td colspan="2"><p>
  <input type='file' name='img1' size='55' id="img1"/>
</p>  </td>
</tr>
<tr>
  <td colspan="2">Banner 2</td>
</tr>
<tr>
  <td colspan="2"><input type='file' name='img2' size='55' id="img2"/></td>
</tr>
<tr>
  <td colspan="2">Banner 3</td>
</tr>
<tr>
  <td colspan="2"><input type='file' name='img3' size='55' id="img3"/></td>
</tr>
<tr>
  <td colspan="2">Banner 4</td>
</tr>
<tr>
  <td colspan="2"><input type='file' name='img4' size='55' id="img4"/></td>
</tr>
 
<tr>
<td><input name="enviar" type='submit' id="enviar" value='enviar' /></td>
</tr>
</table>
 
</form>
 

resultado

Código PHP:

<?php
if(isset($_POST['enviar'])) {
$img1 = $_POST['img1'];
$img2 = $_POST['img2'];
$img3 = $_POST['img3'];
$img4 = $_POST['img4'];
$numbanners = 4; //numero de banners que se rotarán
$random = rand(1,$numbanners);
 
$img = array();
 
$img[1] = $img1;
$img[2] = $img2;
$img[3] = $img3;
$img[4] = $img4;
}
echo "<img src='$img[$random]'>";
?>
 

problema:

Código PHP:

Notice: Undefined index: img1 in C:\wamp\www\banner\sitio.php  on line 3
 
Notice: Undefined index: img2 in C:\wamp\www\banner\sitio.php on line 4
 
Notice: Undefined index: img3 in C:\wamp\www\banner\sitio.php on line 5
 
Notice: Undefined index: img4 in C:\wamp\www\banner\sitio.php on line 6
 

solucion?