As close to a designer tool as batter 
As designer when I'm trying to implement my design in Kibana's Canvas I would like images to be exact same size in order everything to fit in as I imagine/design it.
You can help by giving us options/tools like:
- In fill mode add "Original image size" option
- Button to fit the image to current box
- Button to fit the box to the current image
- Options for adding exact dimensions - WIDTH x HEIGHT (not only for images but all elements)
- Hitting DEL button to delete element
- Grouping elements would be highly appreciated -> and further that aligning those elements.
- Undo and Redo are very much anticipated but I guess there is already ticket for this
Checkbox with resize on upload its not very good idea, I'm not sure what will that help since we can already scale the image and it doesnt matters.
Honestly I'm surprised from your fast response in a good way of course.
I'm new to Kibana and already got hooked.
Cheers,
Gorast