I wouldn't be surprised if Malware creators exploit this since most people don't yet have this plug-in. I.e. someone lands on a page with images they would like to see and have to download and install this browser add-on, but instead of getting the plug-in, they end up installing a piece of Malware.
As for the people who upload their pictures without thinking about the consequences, how likely are they to think of using this add-on, let alone pay for it?
Also, those who want to save an image will quickly realise something is not right when they try opening it outside the browser and decide to resort to the print-screen trick.