how to read .jpeg file extensions from a folder?

public void GetFiles(string path)
        {

            if (File.Exists(path))
            {
                // This path is a file
                ProcessFile(path);
            }

            else if (Directory.Exists(path))
            {
            {
                // This path is a directory
                ProcessDirectory(path);
            }

        }

        public void ProcessDirectory(string targetDirectory)
        {
            // Process the list of files found in the directory.
            string[] fileEntries = Directory.GetFiles(targetDirectory);
            foreach (string fileName in fileEntries)
                ProcessFile(fileName);

            // Recurse into subdirectories of this directory.
            string[] subdirectoryEntries = Directory.GetDirectories(targetDirectory);
            foreach (string subdirectory in subdirectoryEntries)

                ProcessDirectory(subdirectory);
        }

        public string ProcessFile(string path)
        {
            FileInfo fi = new FileInfo(path);
            string sExtension = fi.Extension;

            return sExtension;
        }