Judging from his appearance, he comes from the north.非谓语要看HE吧？他应该是被JUDGE，应该

倒装省略BY
He comesfrom the north (By) judging from his appearance.

这是独立主格结构，judge的主语是we或I，后半句的主语是he，主语不同所以用独立主格结构，开头用动词的分词形式

从外表上看。。相当于固定搭配，judging from 用作独立结构，即不用考虑从句和主句逻辑关系的一致性，用法相当与：generally speaking, considering (考虑到）

judging from= judge by