Is it possible for my image watermark to be read, altered or removed?

Question

Is there a tool that would reveal whether an image contains a watermark and read, alter or remove a watermark if used by someone who is not the creator of the watermark?

Edit to try to reflect Kerzin's intent, as indicated in the comments: This is not for the purpose of knowing how to do it, but whether it can be done by others to remove watermarks from created images, and how it can be made more difficult.

Answer 1

Most of the time you won't be able to remove the watermark. Not even manually.

Unless it is a real simple and/or badplaced watermark and the image itself is easy to reconstruct too.

There are a few tools that claim to be able to remove watermarks but I don't know of any which really are up to the task

Answer 2

In general:

• to detect a watermark that is not visible to the naked eye you need to have some idea of the encoding scheme
• it is possible to come up with a watermarking scheme that yields a watermark one cannot read or definitively confirm the presence of without knowing a secret, however in general that is not the purpose of a watermark
• a watermark that does not distort the image sufficiently to be obvious to the naked eye should in general be removable by manipulations that similarly do not degrade the signal sufficiently to be obvious to the naked eye; however, coming up with the required manipulations may be hard and will certainly require specific knowledge of the watermarking scheme.

Answer 3

It depends on the type of watermark you're creating. I'm assuming you're talking about an opaque or semitransparent logo or text that is usually placed in a corner of the image.

There is a balancing act here. If the watermark is small enough, users can always just crop it out. But if you make it too large, you make the image unusable. Sometimes this is the intent (for example, look at iStockPhoto.com: they use big watermarks over the center of the image so that you can't use the image without buying it). Other times, you don't want to do this (say you're posting a wallpaper to DeviantArt: you still want people to use the image, but no one's going to use it if the watermark takes up a third of the screen).

If the watermark covers a part of the image that is not too detailed, users who know what they're doing can use the clone brush or other tools to photoshop it out of the image. (The same way I once removed ugly power lines from an otherwise beautiful sunset photo.)

Also, if the watermark is in the same place on all images, and it is transparent enough, sophisticated users can build a filter based on the common pixels from several of your images. In the right circumstances, such a filter can work like magic. (But usually it won't.)