CopyToOneDrive.cs

using System.IO;
using System.Linq;

namespace CopyToOneDrive
{
    internal class Program
    {
        private const string _destination = @"C:\Users\YourUserName\OneDrive\Camera Roll";
        private const string _source = @"D:\Camera Roll Backup\";

        private static void Main(string[] args)
        {
            var files = new DirectoryInfo(_source).GetFiles();

            foreach (var file in files)
            {
                var oneDriveFiles = new DirectoryInfo(_destination).GetFiles();

                // Don't store files using __highres in OneDrive
                string filename = file.Name.Replace("__highres", "");

                if (!oneDriveFiles.Any(x => x.Name == filename))
                {
                    string highResFileName = file.Name.Replace("Pro.jpg", "Pro__highres.jpg");
                    string highResFullFileName = Path.Combine(_source, highResFileName);

                    // Choose the high res version if there is one
                    if (File.Exists(Path.Combine(_source, highResFileName)))
                    {
                        File.Copy(highResFullFileName, Path.Combine(_destination, filename), false);
                    }
                    else
                    {
                        File.Copy(file.FullName, Path.Combine(_destination, filename), false);
                    }
                }
            }
        }
    }
}