Xcode won't remove Derived Files

Check your "Copy Bundle Resources" in Build Phase, You should find some files(should be images in your situation) in that list twice. Delete them and rebuild.

It is ok to delete DerivedData folder, you can delete all files from DerivedData sub-folder (Not DerivedData Folder) directly.

That should not take any effect. Contents of DerivedData folder is generated during the build time and you can delete them if you want. It's not a issue.

All contents of DerivedData will be recreated when you build your projects again.

I suggest you clean project project and build again, ALSO PLEAE MAKE SURE YOUR DELETED DerivedData folder is not in BIN please clean trash, it is important