Your question: Why do I have to add keywords to my images?

Answer:
Keywords enable customers to search for images matching their specific requirements.
We require a minimum of 10 keywords for each image.
Keywords will describe the content of the image as well as any feelings, moods or abstract concepts that you feel apply to your image. Try to use single words separated by commas. If there are important words in your title or description, don't forget to include these in your keywords as well. Avoid misleading keywords and use a spell checker if necessary.

Bear in mind that we serve an international audience, so you may want to account for spelling variations between countries that speak the same language. “Colour” and “color” are examples of variations between U.S. and British English. Also, people who speak U.S. English tend to use the letter “z” where the British use the letter “s”. “Realize” and “realise” are good examples.