Some may even download an app that allows them to edit their photos before uploading them onto social media sites such as Facebook, Twitter and Instagram (which is becoming more common). There are several ways that people use these apps – some will just use one for personal viewing, while others will download an app specifically designed for sharing pictures with friends and family. Whether you have hundreds of photos stored on your phone or tablet, or just want to look back at some from the last holiday, it can be useful to have a way to view them quickly and easily. There are many reasons why you might want to use a photo viewer app.