Hi, thanks for posting your question.
You're right in that you can't remove certain folders from Windows Photo
Gallery. Specifically, the help topic for Photo Gallery says this:
You can remove folders that you have added to Photo Gallery at any time, but
you can't remove the folders that are in Photo Gallery by default.
In addition, you can't remove a subfolder without removing its top-level
folder as well.
So in your case, since Pictures is in the Gallery by default, it can't be
removed. In addition, you can't remove a subfolder of Pictures. To read the
entire help topic, go here:
The only solutiuon to your problem that I can think of is that you could
keep photos you want to exclude from appearing the Photo Gallery in a folder
that lives outside of Pictures.
I hope this information helps.
Windows User Assistance team