Don't delete all of your photos!
It's a combination of things, mostly related to editing and some of the new camera formats in iOS 8. The "local disk" files contain metadata about some of the special formats.
1. Go in to Settings, Safari, Advanced, Website Data, Remove All (many of the "local disk" files will go away)
2. Browse the DCIM subfolders and identify the folders that have "local disk" files in them. The folders with one or more "local disk" files have one or more of the following:
- Edited photos
- Time Lapse or Slo-Mo videos
- Burst photos
For Edited Photos, you need to find them in the folders (you can compare edited date to created date), then edit the photo on the iPhone and REVERT to the original photo. Note that you must unplug the iPhone (haven't tried an iPad) from the computer and plug it back in before the "local disk" files actually disappear - refreshing the folder with F5 doesn't get rid of them.
For Time Lapse or Slo-Mo videos, the only solution I've found is to manually copy them off of the iPhone and then delete the .MOV file(s), then unplug/re-plug.
For Burst photos, open the Burst package and select all of the photos in the Burst (or delete the ones you don't want, selecting the rest). And, unplug/re-plug.
After doing these 4 things, all of my "local disk" files were gone.
(PS - I managed to look inside of some of the "local disk" files and they seem to contain a modified XML structure. Why Apple doesn't just put an XML file in the folder that is standard and able to be recognized by Windows, I have no idea. . .)
Good luck!