iOS 11 introduced a default image format when taking pictures, which is HEIC and HEIF.
These images will not work with the POA Photos App. The only file extensions you will be able to upload are jpg, jpeg, and png.
The other option is to disable HEIC if you’re facing problems. This will force iOS to store all images as JPEG. You can disable HEIC from settings > camera > formats.
* High-Efficiency Image File Format (HEIF)is a file format for individual images and image sequences. It was developed by the Moving Picture Experts Group (MPEG) and is defined by MPEG-H Part 12 (ISO/IEC 23008-12). The MPEG group claims that twice as much information can be stored in a HEIF image as in a JPEG image of the same size, resulting in a better quality image.