いくつか置いておきます
/* 1012 最上義光 */
img[src$="background/1012_QOkAhV3b.png"] { background: url("http://img593.imageshack.us/img593/3434/10362752.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="1012_QOkAhV3b.png"] { background: url("http://img139.imageshack.us/img139/3344/91qsmollpng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3010 本願寺 */
img[src$="chara/3010_nx8jlzyr.png"] { background: url("http://img225.imageshack.us/img225/2081/18001111.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3010_nx8jlzyr.png"] { background: url("http://img30.imageshack.us/img30/6572/57qsmollpng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3015 鍋島 */
img[src$="background/3015_s1yB01ye.png"] { background: url("http://img821.imageshack.us/img821/9426/74182483.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3015_s1yB01ye.png"] { background: url("http://img14.imageshack.us/img14/7505/38smollpng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3018 馬場 */
img[src$="background/3018_NjglSoBb.png"] { background: url("http://img833.imageshack.us/img833/3156/85976382.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3018_NjglSoBb.png"] { background: url("http://img16.imageshack.us/img16/7026/79qsmoopng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3021 長野 */
img[src$="background/3021_z6z5e5K9.png"] { background: url("http://img843.imageshack.us/img843/6004/70284796.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3021_z6z5e5K9.png"] { background: url("http://img571.imageshack.us/img571/5374/95qsmoll.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 1012 最上義光 */
img[src$="background/1012_QOkAhV3b.png"] { background: url("http://img593.imageshack.us/img593/3434/10362752.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="1012_QOkAhV3b.png"] { background: url("http://img139.imageshack.us/img139/3344/91qsmollpng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3010 本願寺 */
img[src$="chara/3010_nx8jlzyr.png"] { background: url("http://img225.imageshack.us/img225/2081/18001111.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3010_nx8jlzyr.png"] { background: url("http://img30.imageshack.us/img30/6572/57qsmollpng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3015 鍋島 */
img[src$="background/3015_s1yB01ye.png"] { background: url("http://img821.imageshack.us/img821/9426/74182483.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3015_s1yB01ye.png"] { background: url("http://img14.imageshack.us/img14/7505/38smollpng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3018 馬場 */
img[src$="background/3018_NjglSoBb.png"] { background: url("http://img833.imageshack.us/img833/3156/85976382.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3018_NjglSoBb.png"] { background: url("http://img16.imageshack.us/img16/7026/79qsmoopng.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
/* 3021 長野 */
img[src$="background/3021_z6z5e5K9.png"] { background: url("http://img843.imageshack.us/img843/6004/70284796.jpg") no-repeat !important; width: 0 !important; padding: 315px 224px 0 0 !important; }
img.smallcard_chara[src$="3021_z6z5e5K9.png"] { background: url("http://img571.imageshack.us/img571/5374/95qsmoll.png") no-repeat !important; width: 0 !important; padding: 162px 116px 0 0 !important; }
回答よろしくお願いします!
http://blog.goo.ne.jp/libera2736/e/b78980d3e89c18fe01406e0a8cd381e7
を読んでみてください。上手くいかない場合はその次の記事を参考にして頂けるとなんとかなると思います
もう1つ質問なのですが、
自分で変更後の画像などを用意したいときの方法などについては
どこか参考にすればいいページはありますか?
画像加工 等で検索をしてみると何か自分に合った良いものが見つかるかもしれません