After double checking all my NTFS user and group permissions and removing read-only from some folders, I still couldn't save files to my Pictures folders and other folders... No idea why, everything looked good!

Luckily I found the following page and now I can finally save files to my user folders (like Pictures) again without "Permission Denied" errors.

Copy paste from: https://www.reddit.com/r/Windows10/comments/3g42rn/updated_to_windows_10_now_im_getting_access/ctv0oo0

Here is what I did to fix the same issue on my Win7 upgrade. I am pretty sure the problem stems from OneDrive somehow resetting permissions incorrectly on startup. For me it was my Pictures folder on my account (and One Drive Picture folder) that was causing issues (i.e. I lost permissions).
Disabled sharing for both Picture folders
Ran these commands from administrator command prompt (xxx is user name)
cd /users/xxx
icacls Pictures /reset /t /q (this will reset all the permissions on Pictures folder tree to default)
cd /<onedrive folder> (i.e. cd to base OneDrive folder)
icacls Pictures /reset /t /q
reboot
Note: If it still doesn't fix it then repeat the above, and disable OneDrive until MS gets it sorted.

Peace!

Devvie