How does youtube's report bug tool takes a screenshot of you screen?

Question

If you go on the bottom of the page there's a "Report bug" link.

They let you highlight parts of the screen and sent it along with the bug description.

Any idea of how this could be implemented?

Answer 1

It uses Google's Feedback tool, which is a heavy implementation of JavaScript.

Taking a look at their script, they even have a JavaScript-ported version of a JPG encoder that they use to render the user-modified HTML page into an image, which I assume is then AJAX'd on over to Google when the user hits send.