A new feature and a new plugin are now available and they work together very well!
The new feature is Hotlinking Protection. This feature allows you to protect resources from your website that may have been embedded in a foreign website, without your consent. You can then simply stop serving those hotlinked resources (a forbidden status is returned), or you can decide to serve different versions of them...
And this is where the new plugin becomes handy: the Spincast Watermark Plugin. This plugin allows you to watermark files, images in particular. For example, you could use this plugin to create an image identical to a base image but with your logo added at one of its corners.
Hotlinking protection and watermarking go very well together, as you can now easily serve a watermarked version of your images if they are hotlinked without your consent.