This is very easy and should be well know the Watermak image. There is a Topic in our FAT forum on this. Just upload
your watermark.gif or watermark.png image to your site to auction/theme/default/images and it will apply to
the new auctions but will not apply to already posted auctions.
Of course if you do not want watermark at all, just delete these files watermark.gif, watermark.png from
auction/theme/default/images
on your site.
Thanks
Mewsoft Support www.mewsoft.com