We have a topic on our FAQ forum on watermark.
You have to upload your own watermark.gif file to auction/theme/default/images folder, it will replace the default watermark
which comes with the software, if you do not want watermark at all, just delete the file watermark.gif (and watermark.png if exists) from the folder:
auction/theme/default/images
Thanks
Mewsoft Support www.mewsoft.com