君にもできる！ブックマークレット制作講座 ref: http://qiita.com/YSRKEN/items/162c82d081387c4d4603

sample1.js

javascript : (function (){
    var url = location.href;
    var pos_id = url.indexOf('im');
    var id = url.substring(pos_id + 2, url.length);
    location.href = 'http://seiga.nicovideo.jp/image/source/' + id;
    var image_url = location.href;
    image_url = image_url.replace('/o/', '/priv/');
    location.href = image_url;
})();

sample2.js

// 展開時
javascript : (function (){
    var str = document.getElementsByTagName('body')[0].innerHTML;
    var posX = str.indexOf('他のイラスト<');
    var posY = str.indexOf('>もっと見る<');
    var posA = str.indexOf('/seiga/', posX);
    var posB = str.indexOf('\"', posA + 7);
    while ((posA !=- 1) && (posA < posY)){
        url = 'http://seiga.nicovideo.jp/seiga/' + str.substring(posA + 7, posB);
        window.open(url);
        posA = str.indexOf('/seiga/', posB + 1);
        posB = str.indexOf('\"', posA + 7);
    }
})();
// 圧縮時
javascript:(function(){var str=document.getElementsByTagName('body')[0].innerHTML;var posX=str.indexOf('他のイラスト<');var posY=str.indexOf('>もっと見る<');var posA=str.indexOf('/seiga/',posX);var posB=str.indexOf('\"',posA+7);while((posA!=-1)&&(posA<posY)){url='http://seiga.nicovideo.jp/seiga/'+str.substring(posA+7,posB);window.open(url);posA=str.indexOf('/seiga/',posB+1);posB=str.indexOf('\"',posA+7)}})();