Adding an original description that describes "WHAT, WHERE, WHEN, and, if appropriate, WHO" is more important than adding tags. Try to describe your image in one sentence. You do not have to repeat words which are already in the title.
If you copy text for your description from Wikipedia, you must include a citation and a link to the original page on Wikipedia. However, copying text from another source like Wikipedia will hurt your search engine page ranking, so we don’t recommend it.