Instagram is a vintage photography smartphone app that allows you to share and take images. In order to use this app you have to create a free account. Why you may ask? Because Instagram is also a popular social network. On Instagram you can follow other users' photo streams and you can be followed in return and by other users.
Pinterest is based on the bulletin board or scrapbook concept where people collect images that inspire them and pin them to their pinboard. Pinterest is a relatively new platform which was launched as a beta in 2010. It has subsequently become one of the more popular means of social networking. People can search on the Pinterest site for others who have interest in images from similar categories. Users can "repin" images from others' pinboard. The images are categorized in popular categories such as travel, cars, food, film, etc. Again there is a question of copyright when it comes to use of images on Pinterest created by a third party. Stumbled Upon StumbledUpon is a social media platform that is similar to a search engine like Google. The main difference is that it is user generated recommendations, which allow users to share or recommend other web pages, images, videos, based on one's personal interests and tastes.