Project sentry gun is an open source project for people who like to make sentry guns. From the looks of it the most popular flavor is for paintball guns, but you could adapt this design to anything — as all the basics are there. The project is powered by an Arduino or a custom Sentry controller, some servos, webcam, and some raw materials.
The site has everything you need, part’s list / BOM, places to order the parts, schematics and source code. They also have the design for their standalone controller. You can even buy a complete setup.
Cool project, looks like it could be a lot of fun.