At this point in time, you cannot link directly to an image because clicking on an image will display it in large size.There are maybe two workarounds I can think of. 1.) insert a QR code into the image.However, this would only work well with mobile devices. 2.) Install a "button" below the picture, which then contains the "link".
But you are right to have the capability to edit HTML would be very interesting! Maybe someone else has a better idea, but that are my thoughts so far. Hope it helps.