Watermarks are placed on copyrighted images like stock-photos in order to keep people from using them without permission or without paying. And manually removing them requires Photoshop skills, time and being ok with the image not looking its best post-removal. But Google has found a way around watermarks -- work it recently presented at the Computer Vision and Pattern Recognition Conference.
The trick is to take lots of images -- we're talking hundreds or thousands of photos -- with the same watermark and use software to detect repeating structures. With enough examples, the watermark becomes the signal and all of the photos become noise. The watermark pattern can then be removed in totality from the image without reducing the quality of the image itself.
However, along with its method of seamlessly lifting watermarks, Google also provides a way to counteract it. Changing the watermark's position on the images randomly for each photo doesn't stop the software from doing its thing, nor does changing how opaque the watermark is. But randomly warping the mark just slightly for each image does prevent the program from removing it in full.
Google says it's definitely possible that someone will find a way around the warping method in the future, but these methods and the use of randomization could be helpful to photography and stock image communities.