It seems the problem here is that the watermark is transparent, and thus still contains information about the original image. Similar to how if you want to censor a part of an image, you should always use a single solid color because e.g. a blur can be inverted. But I guess that would degrade the quality of the watermarked photo too much.
The watermark has to overlay the important parts of the image (otherwise, overlaying your own watermark, or simply cropping it out, becomes trivial). It has to be transparent, because the purpose of having the image available in the first place is that potential customers must be able to evaluate it for their purposes before purchasing a license for it. Slapping a solid color bar across it makes that quite difficult.