I have a request related to image size: it would be very useful to have a checkbox titled "Lock aspect ratio" near the image size fields (see image), so that WireframeSketcher would lock the image aspect ratio. If you enter a new width, height would be adjusted accordingly (and vice versa).
I know you can resize the image while keeping the shift key down (this will maintain the aspect ratio). However, it would be much easier to get an exact dimension by entering it numerically instead of dragging with mouse.