def copySnapshots(df_in, snapshots_dir, output_dir):
    if not os.path.exists(output_dir):
        os.mkdir(output_dir)
    swc_files = df_in['swc_file_name']
    if len(swc_files) > 0:
        for afile in swc_files:
            filename = snapshots_dir + '/' + afile.split('/')[-1] + '.BMP'
            if os.path.exists(filename):
                os.system("cp  " + filename + "  " + output_dir + "/\n")
    return