What does a vertical line to the left of multiple staves indicate to a musician?

It depends if it's a single or a double bar line. 
if it's a double bar line it's just there to separate the sections of the music and if it's a single bar line all it does it separate the beats in order to make a measure.  

Idk but maybe a camera?

Answernon-religious themes became more popular, and people also wanted to show off their wealth because painting was a sign of this at the time;