Backdrop

Backdrop helps you check if there are any bad pixels on your monitor and covers your entire desktop with a blank window to prevent others from accessing your files.

You can easily change the way the application operates from the program's Preferences screen and choose the preferred desktop cover image from your local folders.

The utility doesn't bring you an actual interface. Instead, it gives you access to a Preferences panel where you can configure various settings according to your needs. Backdrop applies any desktop image changes as soon as you alter them.

You can cover your desktop with a blank window showing any color you like (you can use Mac's default palette tool to choose the shade) or any picture from your local directories. The application lets you choose from various display modes (Center, Stretch To Fill Screen, etc.), adjust the opacity level of the colored window, and select the monitors where the desktop cover should be displayed.

Also, Backdrop works with a wide variety of image formats and provides you with multi-monitor support.

My only issue with this program is the fact that it lacks an option to define global hotkeys for showing and hiding desktop covers.

As for the rest, I think it does an incredible job and it's definitely worth installing it on your Mac, especially since Backdrop is free of charge.