Thanks, but that is already what I've tried to do: Using the usual Windows Explorer files view to drag (right-click, Copy or Move) the image files from the phone to a folder on my computer. Performance has consistently been inconsistent and unreliable.
The native camera on an iPhone 7 is not an "app"; it does not appear as an app in iTunes, so it cannot be "synched" with the computer.
Having changed the mode from Automatic (as described by others) does not make the process reliable. The file extension seems to be irrelevant. As as far as I can see, the number or total size of files being transferred is also irrelevant. Thinking maybe
that the phone timed out, I transfered in very small batches, even one-at-a-time, no better luck. I typically Move files rather than Copy, so that I can easily see any files that have not been transferred, and so I don't inadvertently delete unsuccessful
files from the source folder. However, after my many unfinished transfers, I wound up with a lot of duplicate files on the target. Usually I choose to skip all files with identical dates and names, but I even skipped each one at a time -- again, thinking
that the iPhone saw the batch skip as a timeout. Still unreliable. Finally, I examined the lists of hundreds of files and after an hour of this nonsense and some manual deletions, got my photos off the phone.
All this is the same for videos, which are similarly stored on the phone in a different folder. For them, I've given up for now.
Microsoft, Apple, this is no way to compute.