By default the iPhone saves photos as HEIC. These originals carry rich information about the device and conditions of capture, which makes good evidence that a person took the photo.
A HEIC original holds EXIF such as device model, lens, exposure and capture time, maker-specific records and sometimes depth data. When these survive and agree with each other they count toward a captured photo. Metadata can be rewritten, though, so it never proves anything alone.
The share sheet, messengers and web uploads convert HEIC to JPEG, strip most of this information and recompress. Such copies have little left to say about their origin, so inconclusive results increase.
Some AI editing features on recent phones record the edit in metadata or a visible mark. When such a record exists it goes into the alteration axis; when it does not, alteration analysis and detectors decide.
For a photo that needs checking, use a transfer that does not convert it, such as sending the original file, file sharing or a cable copy. Scanning the original HEIC as is shows the most evidence.
This is general guidance, not legal advice. A scan result is a probabilistic assessment, not proof.