From an expectation perspective, if I were to blindly (without RTM) develop a client I would expect to GET an image if I used that verb using your REST API, because that is how it is commonly used.
Now in your case you want to deviate from it so it matches your app controller. Well that is fine, especially if you are the only one who will consume the REST API service, but if other people will develop clients for it then I would choose for your first solution if you want to use the REST approach consistently.