Many photographers agree that the commercially produced cameras were the single biggest drive to popularize the art form. The commercial photographic world could include Advertising photography. These are photographs made to illustrate and usually sell a service or product. Photography is used to preserve memories of favorite times, to capture special moments, to tell stories, to send messages, and as a source of entertainment. Photography as a usable process goes back to the 1820s with the development of chemical photography. Photography is a unique and creative medium of self-expression. "One picture is worth a thousand words," which has an interesting basis in the history of photography. Photography can also be viewed as a commercial and artistic endeavor. The aesthetics of photography is a matter that continues to be discussed regularly, especially in artistic circles. Portrait and wedding photography is typically photographs that are made and sold directly to the families of the people in the images.