Instafeed exclude by tag or post

I would like to exclude certain posts from the Instafeed. Either by tag or by some post ID. I know how to apply a filter that let's only pass images specified by tag:

  filter: function(image) {
    console.log(image);
    return image.tags.indexOf('thisTagPasses') >= 0;
  }

However, I have no idea how to exclude/skip certain images. Any idea's?