Press the Share button on your DS4 after setting up a photo. You'll get a menu where you can either upload it directly to Twitter/Facebook and so on, or you can save it directly on your PS4 system. Most photo sites feature compression, meaning you'll lost some image quality. From what I gather, the best way to share your pictures with people, is to save it on your system, then transport it manually via a USB stick, and then finding a site that won't compress the file.