message: Auto-guess format of thumbnail from .jpg file extension
diff: @@ -268,6 +268,8 @@ struct ThumbCommand : public Command
  type = FileType::TGA;
  else if(dot != NULL && strstr(dot, "bmp"))
  type = FileType::BMP;
  + else if(dot != NULL && strstr(dot, "jpg"))
  + type = FileType::JPG;
  else
  std::cerr << "Couldn't guess format from '" << outfile << "', defaulting to jpg."
  << std::endl;
  