Taking screenshot using javascript for chrome extensions

Since you're using this in Chrome Extensions, the Tab API has a method called captureVisibleTab, which allows captures the visible area of the currently selected tab in the specified window.

To use that you just add "tabs" to your permissions manifest. And from your background page, or popup (or any other extension page), you just call that method like this:

chrome.tabs.captureVisibleTab(null, {}, function (image) {
   // You can add that image HTML5 canvas, or Element.
});

You can control the property by adding {quality: 50} and change the format too, all described within the docs mentioned above.

The beauty of HTML5, you can alter that image with HTML5 Canvas, you can manipulate, transform, modify, clip, anything you want, very easily!

Hope that is what your looking for! Happy New Years!

I'm not sure if this was available when the original answer was given, but Google now has an example available that shows how to take screenshots:

http://developer.chrome.com/extensions/samples.html

Search for "Test Screenshot Extension" on this page.

UPDATE: Here's the new example using the desktopCapture API:

https://github.com/GoogleChrome/chrome-extensions-samples/tree/main/apps/samples/desktop-capture