Amazon is offering 50 free 4×6″ photo prints for Prime members to help promote their Amazon Drive. No, that's not their new line of autonomous vehicles, but instead a photo storage platform. Non-Prime members will have to pay $4.99 for shipping, but you can get around that by using your free Amazon Prime trial if you haven't already! Don't forget students (or anybody with a .edu email address!) also get a free Prime trial.
When they first offered this freebie in September 2016, it also signed you up for a free 3 month trial of Amazon Drive, BUT you could immediately tell Amazon not to charge or renew your account. I'm not 100% certain if they're doing that again this time around, but just in case they are, you can cancel the auto renew by logging into Amazon Drive then clicking on the “do not continue” link.