No statement of copyright ownership is required by law, and its absence does not weaken the protection of copyright. But it is still a good idea to include one in order to counter someone arguing that they were unable to find out the copyright status of the work or whom to ask about permission. Images whose rights status and ownership cannot be determined are called 'orphan works'. The copyright statement should appear on the same page as the image on the web, on the back of prints, and also in the metadata of all image files uploaded or emailed anywhere.

In UK law and most other countries, a copyright statement is not formally required, but if you use one (and you should) a valid copyright statement comprises 3 essential elements

• © - the international copyright symbol
• Your name - the copyright holder's name
• Year - the date of first publication

So © John Doe 2008 is correct. You may add other information as well, such as 'All Rights Reserved', a telephone number, address, website address and so on. EG © John Doe 2008 All Rights Reserved - www.johndoephotos.co.uk

Metadata is textual information embedded in an image file. Not all image file formats are capable of holding metadata, but JPEG, TIFF, PSD and most digital camera RAW formats support it.

Metadata text is only viewable in programs that are capable of displaying it. Photoshop and most advanced image editing and management tools have the capability.

There are two common formats for metadata, EXIF and IPTC. EXIF is most widely used for recording information at the time of exposure. IPTC information is added later.

IPTC information is the standard location for the copyright statement, along with contact details and other information relevant to the image. Neglecting to embed a copyright statement in a file can lead to it becoming untraceable and an 'orphan work'.

Deliberately altering copyright metadata is an offence under UK and US law.

Altering or removing copyright ownership information, in IPTC or anywhere else, is a criminal offence in UK under the 1988 Copyright Designs and Patents Act if done with the intention of depriving the rights holder of their intellectual property rights. However the practice is commonplace among publishers, who then fail to seek permission or pay the unknown rights holder, or syndicate the material as their own. Prosecution is virtually impossible since intent would have to be proved.

Altering other metadata such as captions may also be unlawful, contravening the author's moral rights if they have been asserted. 

The short answer is that you cannot. The only certain means of making sure your work cannot be copied is to keep it off the public web, and never allow any copies into the hands of someone who might publish anywhere. Anything that gets printed is quite likely to end up on the internet.

Some people advocate technical tricks such as slicing your image into lots of small pieces and having the browser reassemble the parts for display. This certainly makes 'saving'  from a browser hard work, as there are many parts that need to be saved. But a simple screen grab defeats all that completely.

The same applies to web authoring techniques that place the image in the background of a table or layer, and also disabling the right mouse button ability to save a file. The latter is especially annoying to Windows users who will find all their other right button options inaccessible too. Neither method will deter any but a casual user who isn't trying very hard.

Likewise, embedding your photos in Flash presentations or Acrobat PDFs offer little protection. Tools to capture and extract from these documents are freely available on the web.

And anyway, if it can be seen it can be screen captured. Visible watermarks are currently probably the most effective deterrent, if you find their appearance acceptable.

Watermarking can be of two types, visible or invisible.

Visible watermarking - where you emblazon '© John Doe 2008' across the image - has the obvious problem that it spoils the picture. Watermarks like this also are usually quite easy to edit out unless large and intrusive and placed across the most important parts of the photo. They are however a clear and simple warning, and worth thinking about.

Invisible watermarking uses steganographic techniques to invisibly embed a hidden, registered creator's code in the image itself. This technology is offered commercially (and at quite high prices) by Signum and Digimarc, among others. The theory is that their hidden code can survive multiple Photoshop procedures or even printing on a commercial press, so images can always be traced back to the rights owner. In practice there are methods for attempting to corrupt the code, and questions about how robust such watermarking really is. It also degrades image quality to an extent that some find unacceptable.