the headers already sent error means there is output to the page between php tags. The error is reporting the problem around line 20:
output started at C:\xampp\htdocs\Petseen\ShopAdmin\shop_Insert.php: 20
at line 18 - 20, you have:
?>
<?php?>
<?php
change that to:
?>
<?php
on the results page, you need to convert the code that displays the file name to an image tag:
<td class="WADAResultsTableCell"><?php echo($row_WADAshop['productImageSource']); ?></td>
should be:
<td class="WADAResultsTableCell"><img src="../Shopimages/<?php echo($row_WADAshop['productImageSource']); ?>" /></td>