The photos you post via e-mail (such as from your phone) or through the mobile app need to arrive to the system with the correct horizontal or vertical orientation. Many phones can detect whether you are taking a picture horizontally or vertically and will send the picture appropriately.
However, some cameras and phones do not have motion sensors. In these cases, you will likely need to take all photos with a horizontal orientation or head to the full website to upload the pictures.
In the Project Photos page of the website, you will be able to rotate images on a picture-by-picture basis prior to uploading.
Once a photo has been uploaded to the system, there is not a way to rotate the image.