When trying upload "drag & drop" image jpg at pimcore admin panel into assets this pops out:
Whoops, looks like something went wrong.
(1/1) NotEncodableValueException
Below is the error image
If you look deep into screenshot you will find this line failed to open stream, permission denied.
You can give permission like this
sudo chmod 777 -Rf /var/www/html/pimcore/web/var/assets/
Do let me know if it gets solved.