Your file's description should be written to provide the client with any extra information they may need to know not already provided by the title and keywords. At a minimum, the description must be in English and include information about the image content. You may include information about where, when, and how the image was created. In some cases - artwork in the public domain for instance – you must also include additional information describing the content and its copyright-free status.
If you'd like to provide your description in another language in addition to English, you are welcome to do so, provided it does appear in English as well.
Beyond that, you are welcome to include additional content. Many contributors like to use the description field to link other images or lightboxes that clients might find useful. As long as the description includes the important information described above, these links and banners are perfectly acceptable.
The description field may not include the following:
4.0 Quality Standards
6.0 Title, Description & Keywords
8.0 Model & Property Releases