How to Format Objects in Google Slides
Images and shapes have some extra formatting options available in the Format Options pane.
The Format options pane opens, displaying a list of categories.
Now, you can adjust the size directly in the top two fields, or by adjusting the scale in the lower two fields.
You can also use this pane to move the image to a specific spot on the slide or rotate it a specific amount.
This is where you can adjust an image's transparency, brightness, and contrast.
You can also apply shadow or reflection effects to images and shapes.