分析All we can do is look at mug shots and stick our fingers in the dam.句子结构

all we can do, 定语从句

is （that）look at mug shots and stick our fingers in the dam，表语从句，省掉了that

整个句子是主系表结构
all we can do 为主语从句
系动词is
两个并列表语从句 look at mug shots 和stick our fingers in the dam.

All we can do is (to) look at mug shots and (to) stick our fingers in the dam.
主语是all (that) we can do
谓语动词is
这句话是新视野书上的吧。我们所能做的是就是看看这些快照，然后在建筑社会安全的大坝中尽一点自己的力。