Much like Microsoft Office's PowerPoint, Google ... the image that you want to use as your background, click "Select" and it will immediately change the background for the current slide in your ...

If you don't want an image to be completely transparent, add a gradient. Text boxes have a transparent background ...

you can create a consistent background that never changes unless you want it to. If you want to lock images or objects in Google Slides, you can use any of the following methods: Lock objects by ...