Check out the links below to learn how to quickly and easily "mask" an image in Google Docs and Google Slides!
Video: Masking and Cropping Images in a Google Doc or Google Slides (4:28)
To "Mask" an Image in Google Slides:
1. Go to INSERT > IMAGE from the menu at the top.
2. Select or search for desired image; then click
SELECT to insert image onto slide.
3. Click on your image and choose the little down arrow next to the crop tool within the toolbar at the top.