1. judging from / by 是“悬垂分词”。“悬垂分词”用来表示说话人的态度，看问题的角度，或对所叙述的情况进行解释，为句子的独立成分，其逻辑主语常无需与句子的主语一致。

Judging from his accent, he must be from Hunan. 从他的口音判断, 他一定是湖南人。《简明英汉词典》

Judging from previous experience, he will be late. 根据以往的经验来看，他得迟到。《牛津高阶英汉双解词典》

Judging from what you say in your letter, you don't sound well. 根据你信上写的判断，你好像身体不太舒服。《朗文当代英语词典》

Judging by the opinion polls, he seems to be succeeding.  从民意测验来看，他似乎胜券在握。《柯林斯高阶英汉双解学习词典》

Judging by his jovial manner he must have enjoyed his meal. 从他快活的样子看，他这顿饭一定吃得很开心。《朗文当代英语词典》

2. judging from / by 用得最普通，但有时也可用 judged by。请看张道真《英语常用动词用法词典》（1981年9月版P.421）的例句：

Judged by ordinary standards, their quality is good. 按通常的标准来看，它的质量是好的。

Judged by immediate results, they failed completely. 从当时的效果来看，他们是完全失败了。