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Watermarking Images
Last updated: 20 January 2005
Published in:
Managing your digital resources |
Tags:
copyright |
image editing |
A watermark is used to convey indelible information about an image to the audience: this might include the name of the copyright owner, date of creation, a logo, contact details, URL and restrictions of usage. Watermarks assist in controlling the use and distribution of images; the more sophisticated systems can support the tracking of protected images across the web. A watermark however, does not prevent unauthorised use of an image, it only informs the end-user that they are using a protected image. Users can choose to ignore this warning.
Do I have to watermark my collection?
First ask yourself some questions. What is the quality of the accessible part of your collection? Do you think your collection has a commercial value to yourself or others? Is it widely available or do you already control access? Is the work protected by copyright? Can you afford to do it? Do the low-resolution thumbnails require protection or just the high-resolution printable images?
Do copyrighted images need watermarking?
While copyright and watermarking protect the owner by law neither are able to enforce the law. Refer to the first answer above. While a watermark must be applied copyright automatically subsists in an original work; there is no requirement to assert it.
Does a watermark affect the appearance of my images?
There are two main types of watermark, a simple visible mark which overlays the image and an 'invisible' mark. The second method produces a watermark, which has little effect on the appearance of an image but can be detected by optimisation software.
Why have a visible watermark?
It is easy to read the watermark information both in print and on screen. It is relatively cheap and easy to apply, but can be difficult to remove. Images with visible watermarks are almost impossible to use undetected while images with concealed marks can escape detection particularly in the print form. However, visible watermarks obscure detail and spoil the look of the image, some viewers may be put of a collection of images with visible watermarking.
So are invisible watermarks better?
Yes and no. Because they are invisible they are almost impossible to remove, but watermarked images are not always obvious, particularly when printed. Invisibly watermarked images can be used undetected. Concealed watermarking can be expensive. Images may be degraded, all be it only slightly by the watermark. Because the mark is virtually invisible, high quality images can be made available on screen and print without the need to control access to the files. A concealed watermark can either be applied in a robust way and will normally tolerate extreme image manipulation, such as distortion, blurring, rotation and scaling, or as a fragile mark, which will be damaged with the slightest adjustment. A fragile watermark is used to detect interference in forensic imagery for example, while a robust mark protects usage.
How do I apply a watermark to my image collection?
A visible mark can be applied directly to an image by most image optimisation programs as semi transparent text or graphic. Some IMS applications will apply watermarks on the fly. As this is generated on demand, data can be generated specifically for the end user such as, time of download, agreed rights of usage and end user details. On the fly or dynamic watermarking requires sophisticated and therefore expensive delivery systems.
Concealed watermarks normally require the user to register with the manufacturer before they can start protecting their work.
Watermarks can be applied automatically to images in batches by the main image optimisation programs or using a stand-alone program.
How much will it cost?
While visible watermarking is virtually free, concealed watermarking can cost hundreds or even thousands of pounds every year, depending on the number of images and the level of protection required.
Should I apply concealed watermarks to my master archive?
No. If access to the archive is controlled you should avoid applying any watermarks to your high quality files. While the embedded watermark is virtually invisible image pixels will have been altered.
Are there alternatives to watermarking?
As a watermark is unable to guarantee compliance perhaps it is not worth doing at all, though consider the commercial value of the collection before it is left unprotected. Some archives require users to register before they can access the collection, images can also be protected by disabling the right mouse click (copy) function, pictures can be sliced up or placed in java applets to make copying more difficult. Individual documents can be saved as Acrobat (PDF) files with password protection.
There are also software solutions, which encrypt data; the end user must have a personal 'key' to access the data. These software solutions will also allow the owner to amended or revoked licences after final delivery.
Last updated: 20 January 2005
Published in:
Managing your digital resources |
Tags:
copyright |
image editing |
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