Invisible signature/watermark?

rutt

I don't like the look of signed digital photos, though I do sign my prints. I'd like to embed a watermark/signature in the digital photos I post so I could eventually prove their origin if it ever came up. Ideally, this would be hard to undo and impossible to see. Does anyone know a way to do this?

Shay Stephens

One way is to encode your text or message so that it can be read via processing. You can create nearly black text that sits on top of a black background and then via levels, crank the white point until the text becomes visible and readable. Like this example:




Just crank the levels white point to 25 to see the "hidden" text. My usage is informative and not meant for stealth. So you may be able to see the text before processing depending on the monitor settings. You could be more subtle at the expense of legibility on small text. Using larger text would allow more invisibility.

Another option is to use the Digimarc watermarking system.

rutt wrote:

I don't like the look of signed digital photos, though I do sign my prints. I'd like to embed a watermark/signature in the digital photos I post so I could eventually prove their origin if it ever came up. Ideally, this would be hard to undo and impossible to see. Does anyone know a way to do this?

tlittleton

rutt,

What about the Digimarc plugin for Photoshop? Would that work for you? I think it used to be free to register with Digimarc, but now they charge like $50 to register an ID.

bham

rutt wrote:

I don't like the look of signed digital photos, though I do sign my prints. I'd like to embed a watermark/signature in the digital photos I post so I could eventually prove their origin if it ever came up. Ideally, this would be hard to undo and impossible to see. Does anyone know a way to do this?

If you want to prove a digital file is yours you can put info into the EXIF via Photoshop. It doesn't show up on the print but it stays with the file. Not sure if this helps or is what you are looking for. Also you can make it an action then automate batch process many pictures at once.

Andy

but but but...

bham wrote:

If you want to prove a digital file is yours you can put info into the EXIF via Photoshop. It doesn't show up on the print but it stays with the file. Not sure if this helps or is what you are looking for. Also you can make it an action then automate batch process many pictures at once.

exif can be stripped...

mercphoto

rutt wrote:

I don't like the look of signed digital photos, though I do sign my prints. I'd like to embed a watermark/signature in the digital photos I post so I could eventually prove their origin if it ever came up. Ideally, this would be hard to undo and impossible to see. Does anyone know a way to do this?

Welcome to the problems inherint in digital files.

David_S85

If you upload an image onto a server, is it not date-stamped there? Any re-use (if stolen) would be date-stamped later. I know this is thin proof, but its something.

rutt wrote:

I don't like the look of signed digital photos, though I do sign my prints. I'd like to embed a watermark/signature in the digital photos I post so I could eventually prove their origin if it ever came up. Ideally, this would be hard to undo and impossible to see. Does anyone know a way to do this?

mercphoto

David_S85 wrote:

If you upload an image onto a server, is it not date-stamped there? Any re-use (if stolen) would be date-stamped later. I know this is thin proof, but its something.

Have any idea how easy it is to change the time of files?

David_S85

mercphoto wrote:

Have any idea how easy it is to change the time of files?

Yes, I can do that at will on any machine I own, but how easy is it to change the server dates at Smugmug, or any other services from one's home without admin rights?

luke_church

Hi Rutt,

IMHO it's close to impossible by current techniques.

I would challenge anyone to produce a signature system that can't be broken. 99.9% can be broken trivialy with photoshop.

Lets look briefly at a few options:

- Least significant bit encoding (steganography) gets massacred by compression algorithms or even the slightlest digital transform. By definition this will be very hard to tell the difference visually. Stegano protection depends on the apparent randomness of crypto algorithms to make it difficult to prove that the image has been modified and isn't just random noise.

- Any visible encoding can be stripped out once the attacker has worked out what it is. Shay's method is clever, but could be removed with photoshop. Even if you did something over the surface of the image, a clever imaging person could write a transform that attacked the signature without substantially changing the visual appearance of the image.

- EXIF and parameter encoding can be trivially removed. Illegal parameter encoding may well result in security systems killing your images after Microsoft's embrassment over their GDI+ JPEG decoder.

Essentially any transform that doesn't substantially change the image, can be removed without substantially changing the image.

I was interested in this problem a little while ago and did some preliminary work on 'invariants'. There seem to be interesting possibilities in taking spatial frequency and fractal fingerprints of images. Changing these noticably is likely to disrupt the image significantly. They can also be used as a much more subtle 'sub-encoding' scheme. Markus Kuhn at Cambridge has done some interesting stuff hiding images this way that were then revealed in a Tempest attack.

So I think that property fingerprinting holds the prospect of some promise. It may also allow an automated scanning system for image theft which is always nice.

If you can get me 48 hours in every day, I'd just love to look at it... Maybe one day...

This is all opinions, they may very well be wrong. Please tell me if you think they are.

All the best,

Luke

rutt wrote:

I don't like the look of signed digital photos, though I do sign my prints. I'd like to embed a watermark/signature in the digital photos I post so I could eventually prove their origin if it ever came up. Ideally, this would be hard to undo and impossible to see. Does anyone know a way to do this?