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The Robustness of Digimarc Watermarks

We have made an informal investigation of the robustness of the Digimarc protection scheme in the face of common-place image operations in Photoshop. We used the example Digimarc image available from Digimarc's web site, which measures 215 by 142 pixels.

• Compression Average - watermark becomes unreadable when image is saved as low quality JPEG, even though the image quality is not noticeably reduced.
• Color adjustment and quantization Good - watermark is retained until the image is close to unrecognizable under various contrast, equalization and quantization operations.
• Cropping, Translation Good - much of the image must be overwritten before the watermark disappears.
• Rotation Poor - free rotations of 1 degree completely remove the watermark.
• Scaling Poor - scaling the image down by 15 pixels removes the mark, as does downsizing by only 1 pixel and then applying high-quality JPEG compression.
• Filtering Good - resistance to Gaussian blurring and sharpening filters, and also to addition of noise, is high.

Rotation is a less common image operation, and thus Digimarc's extreme vulnerability to this may not be so important when considering non-hostile users. However, if the watermark can be removed by a small amount of rotation then many non-technical attackers will be able to remove the watermark easily from within Photoshop. The Digimarc method's vulnerability to scaling, on the other hand, is critical to non-hostile users.

In general we worry that the mismatch between technically impressive watermarking feats and valuable watermarking feats can confuse end users. For instance, an impressive demonstration of Digimarc's capabilities could be given by scribbling over most of a watermarked image, and then demonstrating that the watermark remains intact. However, this scribbling destroys the value of the image, and thus there is no particular point in retaining the watermark.