GIMP Version: 2.8.10
Operating System: Linux
GIMP Experience: Intermediate Level

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Hello.
I need to put any text or logo as an invisible watermark in a photo. I need:
* To place the watermark on any position of the photo.
* That it is not necessary to have the original image to recover the watermark.
* Make it possible to recover the watermark even if the photo has been modified

I found this script and explanation in plugin registry:
https://registry.gimp.org/node/21024#comments

but apparently you need to have the original photo to recover the watermark. Also "Fourier Watermark" G'MIC filter, but it only works with text, can not be placed in any position, and I do not know if it works if the image has been modified.

I remember some time ago have been playing with a jpg image and Darktable equalizer, and with an extreme Luminance value (I guess, don't remember) I had seen a watermark. I do not remember how or with which image.

I've seen some tutorials for photoshop, but do you know some way to do it with GIMP?

The watermark as described doesn't work is the image is scaled. Tamper-proof and invisible watermarks require some non-trivial mathematics.

On a side note, with the caveat that I'm not a lawyer, recovering the watermark from the photo just shows you added the watermark, but this is not a proof of ownership since you can watermark a stolen picture. If you want to go to court with some success, keep a higher resolution picture, crop the image slightly, and/or keep other pictures of the same shoot.

Hi ofnuts!

But if you put in your photo the watermark "Creative Commons (by-nc-sa) - by Ofnuts" and then I steal your photo and I sell/publish your photo as if it were mine, it does not make much sense that "my" photo appear labeled as "Creative Commons (by-nc-sa) - by Ofnuts".

So my idea is to put the license and authorship as a visible foot note. But those footnotes can be removed easily. So also I want to put hidden watermarks in important places of the image. Thus for example in a forum I can make clear to others that some user is not in compliance with my photo license writing the instructions: You open the image in GIMP - Do this and that and you can read the watermark.

Here I found this tutorial for photoshop, but I'm not sure how to do it in GIMP (at least the result of what I'm doing is not good):
http://www.cgrats.com/create-an-invisib ... oshop.html

Edit:
I've done it as explained in the above tutorial for photoshop, just obtained better or worse results according to the luminosity/saturation of the area where the text is placed:
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Steps:
Open your image. Type a text in black color. Select the text layer and choose the blending mode as "Color". If text does not disappear entirely, move the text to a better place. You can reduce the opacity of the text layer, but not less than 50%. Then select a layer in layers field and choose "Flatten image". Save/export your image.

To see the watermark:
Open the image you saved. In "Colors" > "Hue-Saturation" put the saturation to the maximum value. Then you play with the "Hue" to see the watermark.
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Aanyway the thread remains open, just in case you know a better technique

This is how I would watermark. Add text, opacity to 50%, layer mode multiply.
Unfortunately any color data is recoverable (eg. watermark removable) if the pixels are visible below the watermark. But in these times and age you need to live with this.

I'm talking in the context of an invisible watermark, and/or a visible one that is easily removed). In both cases I can come up with a picture without any visible marking from you, put my visible copyright on it, and no-one will notice your invisible watermark. Until you come out of the woods with the secret technique to reveal yours... assuming it survived my tampering, because simplistic approaches won't resist simple picture changes (check how your watermark resists a 0.9x downscale).

And assuming your watermark is recoverable, I can still challenge your ownership, because you only proved that you added the watermark to a virgin picture (or a picture with an even more invisible watermark) not that you added the watermark to a picture you own.

Are there any plans to change the way the "Fourier Watermark" G'MIC filter works, so it can be placed in any position? I would like it if it was across the image, diagonally, but other ways would be good too.

@Grits
Interesting question, you could try adding a watermark to a fourier transform manually. Maybe try the gimp plugin here as well as the Gmic one:
http://registry.gimp.org/node/19596 I have my own compilation in linux so I hope that the windows version work.

Starting with your masterpiece http://i.imgur.com/XZCKDVf.jpg,
Apply a direct fourier and hopefully if no defects, you can get a reasonable area to add a watermark http://i.imgur.com/BDUJt3R.jpg
Steer clear of any 'marks' in the fourier map, that includes the center lines. This fourier plugin works with a dark grey, so keep a colour as close to that as possible for your watermark.

Apply an inverse fourier and the result is ok, still on the same original image http://i.imgur.com/JxoWRX4.jpg

Does it survive a save to another jpeg image? Applying direct fourier, and not the same as the original but obvious. http://i.imgur.com/8Z8SkzE.jpg

Does it survive a 80% scale, a small crop and a resave to jpeg. Just about, you might be able to convince the judge that it came from you http://i.imgur.com/yNMf1y6.jpg

Of course, a hidden watermark, same as door locks, only meant for honest people, my web browser has an excellent scrolling capture plugin that defeats this procedure.

Thanks! I have downloaded the plugin and will be installing it shortly.

1) In answer to Grits, above, I understand that the Fourier Watermark is not located in any one place in the image, but distributed everywhere.

To check this I have tried cropping a tiff to quarter size, and it survives clearly in all four corners.
Subsequent rescaling, by a deliberately non-simple ratio, made it barely visible (though by that time I was down to 300px square, so possibly Fourier analysis simply does not work with so small an image - yet to test this theory convincingly.).

2) It seemed better to continue his thread than start a different one so closely related :


My own immediate query which led me to this reading thread is : Should Fourier Watermark survive "jpegging"?
It was perfect on tiff, fine at 100% quality jpg, reduced visibly at 98%, barely visible at 95% and not visible below this. This was on a 1920x1080 px image, maintained at original size.

Am I doing something wrong, that is does not survive jpeg process at normal quality??

(Windows7 64bit, Gimp 2.8.2 64bit from Partha's place with his plug-in package recent version downloaded 1-2 weeks ago)


EDIT
Apologies, just realised I am repeating what what largely said by Rich2005 in June.

Still leaves the question : Should it survive JPG compression?
Not a lot of point if it does not survive the way most people send most things aroud.

These "hidden" watermarks are mostly minute differences with expected pixels values (more or less, twiddling with decimal places). The JPEG compression is also about twiddling the decimal places (ie, mostly removing them...). So it's not surprising that such watermarks don't survive the JPEG compression...

But still, I don't see much purpose in this... because if the WM is not visible to the naked eye, I can slap my own one on the picture, and the general public will only see mine... So the hidden WM doesn't establish ownership for the general public. And to establish ownership in court, there are other and better ways.

what about the record on your home computer showing all the steps in creating your gimp drawing? or is this not enough proof of ownership?

Having your images registered with the copyright office is a way to protect yourself.

There are also IP escrow sites.

Thanks for information Ofnuts