The purpose of creating a Photo Background Helping to Find a Lost Dog Poster is to increase the chances of finding a lost dog by making the poster stand out and be more visually appealing. The photo background helps to draw attention to the poster, making it more noticeable to passersby. This increases the likelihood of someone recognizing the lost dog and reporting information to the owner, leading to a possible reunion. By creating an eye-catching and informative poster, the owner can spread the word about their lost dog effectively and hopefully get it back home.