Transfering all photos via USB cable When I connect my OnePlus One by USB to Windows 7 or Windows 10 (I also tried Ubuntu), I first drag down the notification panel, and then select "File transfers" (I also tried "Photo Transfer (PTP)").

Under Windows I can then navigate to Computer\A0001\Internal storage\DCIM\Camera, and access 236 of my most recent photos and videos. However, I have more photos and videos than this on the phone. If I open the default camera application, and swipe left from the right edge, I can see many more photos - all the photos I've taken in fact. Why does Windows not show me these? Are they stored in another location? Ultimately, how can I tranfer them to my computer.
Option 1.
Look for any software that can help you import the photos from the phone instead of looking for the pictures in directories ##google has a lot of hits. 

Option 2.
Click one those extra pictures, check the details and see the folder path of the file. You can then look for that folder when you connects the phone to the pc.