Pictures of the day will be chosen from Featured pictures of Commons. Featured pictures are the finest images on Wikimedia Commons and are selected by consensus on Commons:Featured picture candidates. Pictures of the day should be selected from images that were strongly supported during the nomination process. For instructions on how to add a Picture of the Day, see Commons:Picture of the day/Instructions.
You can write a description for a Picture of the day by using this function. Replace YYYY with the wanted year, MM with month, DD with day, and xx with your language code. Further information is given on the page that opens after you click on the button.