Digimarc does not place textual information in the meta data of the image file or a visible watermark on top of your image. It actually hides the information inside your image. This technique is called steganography. This invisible watermark is not impossible to detect if you know how to look for it. Below is an image with a hidden Digimarc watermark.
So, you cannot see it, so how can you detect it? There are several ways to do this.
Read Watermark
Load the image into Adobe Photoshop or Elements and use the filter Digimarc and choose "Read Watermark".
Compare
Compare the original image to the watermarked image. If you are a thief chances are you don't have both images, but lets say you do. If you load both images into Photoshop or Elements and subtract the Digimarc image from the Original image and then enhance the result using curves you get something like the following image.
All those colored pixels are the information hidden in your photograph. You can see it only because we enhanced it using curves. If we didn't enhance it then the differences would be pretty minor.
To understand what all those dots mean is another matter and that would require information about the algorithm that Digimarc uses to embed the data which is most likely proprietary.
