An HTML5/JS webcam app.
Create a new S3 bucket. You could use an existing one, but from a security standpoint that isn't a good idea.
Edit your CORS Configuration in the Permissions tab of your new bucket's Properties.
Windows, Mac, Linux, or anything in between? You're covered as long as it has a browser that supports the necessary features.
The app is completely written in HTML5/JS. This makes the app truly portable and private. It also means that you can see all the code right there in your browser.
The app looks at the feed frame by frame. It creates a diff from the current frame and the previous frame. If the diff is beyond the minimum in the app's settings, motion has been detected. Its basic, but it works.
A webcam app is not a novel idea. One that uploads directly to Amazon S3 might be. Local Storage is cool and all but it carries several risks that this app is trying to avoid.
The motion-detected frames are uploaded as soon as they are identified. This is to try and ensure that at least a couple frames are uploaded before someone tries can try to disable(destroy/steal) the device.
This app was built on the shoulders of giants, so why be greedy. Its also all client-side so there is no way to keep it from you anyway. Plus, code obfuscation is lame.