[mastermedo]

Looks interesting. In the beginning I thought it would blur the part of the screenshot farthest away from you and keep the closest thing in focus. But that's not how it works.

I guess it could be useful for focusing on a particular part of the screenshot if you one could mark what the important part is.

[streb-lo]

Click on part of the image to focus it.

[jprete]

Shallow depth of field is used in photography (and movies, sometimes) for exactly the purpose of focusing viewer attention on a specific element or elements.

EDIT: But now that I've looked at the demo...I am not sure what I would want this for.