You’re talking about photos right? Unfortunately you may just have to accept that whatever you do someone will figure a way around removing your logo if they really want. If you’re giving promo pics to affiliates to promote your site I don’t mind discreet logos in the corner, but if it’s too big I might not use it. I also don’t like watermark logos that include the “dot com” or full website address since surfers might type that into their browser instead of clicking on the link I attach to the photo, losing me a sale. And I’m not a fan of models wearing clothing with the logo, or banners on the wall behind the model. I know of one producer who wanted to sell his content but the site name was all over the set so that cut down on the potential buyers.

For videos a small logo in the corner is fine and probably a good idea to prevent piracy on tube sites, although I’ve seen some videos cropped to take out the logo. Including a full screen logo and copyright notice at the beginning and end would probably help. The more editing a pirate has to do to make your video “theirs”, the less they might take the time to do it and leave you alone.