So... I use Google Presentations ALL THE TIME for quick photo editing. My intention has been to make a video about this, but that's still in the pending box. However, I think if you just know that photo editing in GP is a thing then you'll probably figure it out.
Hints for now:
- Crop can crop to rounded edges, circles, and other shapes - very quick and handy!
- Shadows can be great when layering images and text boxes.
- Transparency is another strong tool when creating layered images.
Looking to cut a specific size, like a header image for Facebook, etc??? Screenshot the image in Facebook > create an outline > crop to that exact shape. Super easy.
For mobile while working on desktop > go into Chrome's 3 dot menu > More Tools > Developer Tools. Toggle Device Toolbar. Pick the device you want.
To get your final image(s) go into presentation mode and screenshot it's largest version(s).
With a bit of messing about you'll have a great free image making tool.