Since images are separate from other content like text and tables, the easiest way to make sure the slide looks right with or without a picture is to create two versions of it.
Here’s how that would work:
Slide A: This slide would be your "No picture" version, so you need to apply a conditional formatter like {{booleanValue}:hide-block-if(No)}
Slide B: This slide would be your "With picture" version, so you need to apply a conditional formatter like {{booleanValue}:hide-block-if(Yes)}
This way you make sure your layouts are always perfect.