Web application - Capture a photo?

I have a web application that folks run on both desktops (Mac, Windows), and mobile devices (tablets, phones).

I'd like to capture a photo (with the user's consent of course) in one of the pages of my web app. Tablet and phone users would use the built in camera, and desktop users will use the web cam, if available.

Is there any client-side javascript library that can assist me?