Hi,
I hope you are fine.
1. I am afraid not. Depicter does not have this option at the moment. I will pass this on to our development team as a feature request.
2. Yes of course. Image sizes are responsive meaning that you can resize them for desktop, tablet, and mobile differently. Also, please note that for any slide, you can customize the slide size using the “Customize slide content size” option under the “Advanced” tab on the right-side panel.
Regards