Pixel Perfect plugin makes it easier to develop WordPress sites. Place image overlay over the site which helps with positioning object on the page.
This screen shot description corresponds to /assets/screenshot-1.png. Note that the screenshot is taken from the admin option menu for the Pixel Perfect plugin. You can see available settings.
This is the second screen shot corresponding to /assets/screenshot-2.png. This screenshot is taken from the front-end, showing overlay image over twentyeleven theme with the built in the top right corner. Clicking on this bulb you can switch overlay on/off.