Online collections of photographs including Wikimedia Commons and Flickr contain many images of flowers. Better Homes and Gardens maintains a plant dictionary online that includes photographs and descriptions of hundreds of flowers.
Wikimedia Commons specializes in pictures that are in the public domain or already licensed for all kinds of uses, including commercial use. Flickr allows users to filter searches by type of licensing available, making it easy to find appropriate flower pictures.
Better Homes and Gardens sorts its dictionary by type of plant. Categories include annuals and perennials, roses and houseplants. Each entry features pictures, physical descriptions and information on the plant's ideal growing conditions.