Dragging to resize isn't possible due to the architecture, no. And there's no bug there--it's working as designed. To see more of an image at once, use a different canvas size (possibly combined with a smaller font, if necessary), which you can set in the options menu (F2). As it indicates, restarting RP is required for a canvas size change to take effect. (Also know there are multiple methods for scrolling around images to see different sections of them.)