Portrait (vertical) iOS photos imported into image field rotate automatically to landscape. This image field(s) is on a PDF form the user needs to fill and print. Images will be from Android or iOS depending on the user. Android Portrait photos placed in the same image field are not rotated.
I know this is a very late response to the original question, but hopefully this will help someone in the future....
The issue you’re having is attributed to how Apple devices sets the photo's orientation, and it depends on how you hold the device. As long as you stay within the Apple ecosystem everything seem to works fine. However, when you navigate outside of the Apple ecosystem, the orientation of the device (when snapping a photo) becomes more important.
Basically, the proper way to ensure your photos are always pointing up on import is to take the photo with the volume up/down buttons facing “down” (towards the ground)… this means the iPhone home-screen button (or the lack thereof if using an iPhone X) would be on your right-hand side when snapping the photo. If you take the photo with the iPhone in it’s natural upward position (i.e. volume up/down buttons on left side and the home button on bottom) then your photos will appear sideways on import. Likewise, if the volume up/down buttons are facing up when you take the photos (i.e. home button is on left), then your photos will likely appear up-side down on import.
I learned this after many frustrating hours of research a while back. Same thing happens on iPad.
To ensure correct orientation into your form, I would recommend taking your photos with the iPhone oriented in a landscape position (volume up/down buttons facing down), and that should correct the issue.