Although this fix is for out-of-date oscommerce 2.2 and 4 years overdue, it may be of use for those yet to upgrade.

By default a warning will be shown at the top of the admin when a preview of a product is shown, when the product has not had an image attached or reedited.

The reason for this is the code doesn’t allow for a product not to have an image added at time of editing – ie, if it already has the correct image added to it, no other image would be attached to it, right?

The file to edit is /admin/includes/classes/upload.php

Find:

 } else {
        if ($this->message_location == 'direct') {
          $messageStack->add(WARNING_NO_FILE_UPLOADED, 'warning');
        } else {
          $messageStack->add_session(WARNING_NO_FILE_UPLOADED, 'warning');
        }

Change to:

 } else {
      if (!empty($file['tmp_name'])){
        if ($this->message_location == 'direct') {
          $messageStack->add('search', WARNING_NO_FILE_UPLOADED, 'warning');
        } else {
          $messageStack->add_session('search', WARNING_NO_FILE_UPLOADED, 'warning');
        }
      }

There are several solutions given to this problem – here’s one that is just plain wrong:

http://www.pageonewd.com/local-search-seo/helpful-findings/oscommerce-warning-no-file-uploaded/