Please don't put a comma in front of 'is'.
For example:
"What this picture shows, is the princess in her tower." Bleh.
"What this picture shows is the princess in her tower." Much better.
"More influential than the weather, is the idea of driving two hours with her." Just don't.
"More influential than the weather is the idea of driving two hours with her." Ok.
I couldn't tell you the exact reason why this should be, but when I come across an official explanation somewhere I'll be sure to let you know.
For me, I expect the 'is' to follow directly, and if there is a comma, that sends the signal that something else is going to come first, i.e. "What this pictures shows, in the right corner, is the princess in her tower."
Ok. That's all.
