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Researchers at Google have created an algorithm that can erase watermarks from photos automatically, warning that pictures are vulnerable copyright violations even with superimposed logos used to protect them.
Visible watermarks, the most common mechanism for protecting the copyrights of photographs, are logos or patterns that are overlaid on digital images.
Researchers developed a computer algorithm that can get past this protection and remove watermarks automatically, giving users unobstructed access to the clean images the watermarks are intended to protect.
"As often done with vulnerabilities discovered in operating systems, applications or protocols, we want to disclose this vulnerability and propose solutions in order to help the photography and stock image communities adapt and better protect its copyrighted content and creations," Google said in a blog post.
Manually, the task of removing a watermark from an image is tedious, and even with state-of-the-art editing tools it may take a Photoshop expert several minutes to remove a watermark from one image, researchers said.
However, a fact that has been overlooked so far is that watermarks are typically added in a consistent manner to many images, they said.
Researchers noted that this consistency can be used to invert the watermarking process - that is, estimate the watermark image and its opacity, and recover the original, watermark-free image underneath.
"This can all be done automatically, without any user intervention or prior information about the watermark, and by only observing watermarked image collections publicly available online," researchers said.
"The algorithm produces very accurate estimations of the watermark components already from hundreds of images, and can deal with most watermarks used in practice, including ones containing thin structures, shadows or colour gradients," they said.
"The vulnerability of current watermarking techniques lies in the consistency in watermarks across image collections," they added.
Introducing random geometric perturbations to the watermark - warping it when embedding it in each image - can counter this vulnerability, researchers said.
The technique produces a watermarked image that is very similar to the original photo and will leave very visible traces if removed.
