Partial page obfuscation

Hi, really cool plugin!

I wonder if it would be not too difficult to optionally select an element (or area which then selects any intersecting elements) to obfuscate instead of the whole page.

That would be super useful for screenshots where only a small part of the page is sensitive, e.g. an API credential or an email address, but the rest is what you'd want to show off.

I guess there would be 2 parts to it:

1. some way to select the target/target area
2. dynamically adapting the CSS to make the rules more specific to the targets from (1)

I guess the global obfuscate on/off might still work.