  If the extraction of sensor fingerprints represents nowadays an important
forensic tool for sensor attribution, it has been shown recently that images
coming from several sensors were more prone to generate False Positives (FP) by
presenting a common "leak". In this paper, we investigate the possible cause of
this leak and after inspecting the EXIF metadata of the sources causing FP, we
found out that they were related to the Adobe Lightroom or Photoshop softwares.
The cross-correlation between residuals on images presenting FP reveals
periodic peaks showing the presence of a periodic pattern. By developing our
own images with Adobe Lightroom we are able to show that all developments from
raw images (or 16 bits per channel coded) to 8 bits-coded images also embed a
periodic 128x128 pattern very similar to a watermark. However, we also show
that the watermark depends on both the content and the architecture used to
develop the image. The rest of the paper presents two different ways of
removing this watermark, one by removing it from the image noise component, and
the other by removing it in the pixel domain. We show that for a camera
presenting FP, we were able to prevent the False Positives. A discussion with
Adobe representatives informed us that the company decided to add this pattern
in order to induce dithering.
