If you go into the control Panel / File Explorer Options - View Tab - "Hide Protected Operating System Files" will be unticked.
How ?? - someone will have unticked it (default is hidden). Re-tick it, apply and the folders will disappear along with many others. You can always tell them, they either have "." in front of the name or more easily, the folder will be transparent / Lighter in colour.
Someone at some stage has unticked it. (the box as above)
Altering the files can cause all sorts of trouble, compare it like your Linux OS -- if you go into folders/files that require top level admin rights, a person can really do a lot of damage. ( not a good idea to do it)
The Only Default "Picture" Folder is under the User Name / Pictures.
Try re-hiding the folders, and see if it makes any difference with the external HDD. If the box is unticked it will effect hidden folders on any attached drive /device, phones, cameras included.