If you're using phantom crop the photo to Potrait Rectangle and enable stretch image in settings, crop it correctly or else the stretch feature will overdo it and look suspicious
You need a third party app, but be careful. They banned my 25k Snap for using third party apps. If you root your device try getting a Snapchat modification, so you can upload pictures to your story through Snapchat. Hard to explain but I am sure you will understand if you do some research.
Good luck.