Adding a Watermark to an Image
Suppose you have taken a lot of great photos and uploaded them (as PNG files) to some website which is viewed by many people. If you wish to add a copyright to an image, but don't wish to add visible text to the image then you can add a 'watermark' in the sense of hiding a copyright notice within the image. To do this using Stego PNG first create a text file which has something like "Copyright 2013 Alfredo Xavier Friedrichshofen. All rights reserved." (Adding dire warnings for use without proper authorization is pointless since the text would normally never be read by anyone other than yourself.) Then specify your photo as the input image and give a location and name for the output stego image (as described in Hiding a Data File), then hide the text in the image (and upload it again).
If you later find your photo has been used by someone on some web page (as a PNG file) without your permission then you can download the image and verify that your copyright notice can be extracted from the file, then you can inform the unauthorized user of this.
Your copyright notice can also be in the form of an image file. Hiding an image file is explained in the previous section.
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