Google's apps on Drive just keep getting better and in a recent update the facility to edit images within slides in presentations has been added. They can be cropped, frames and masks applied, and more.
To see the new editing features that have been added, log in to Google Drive and either load a slide show presentation or click the Create button to create a new presentation.
Go to a slide that has an image or click the plus button on the left to add a new slide and choose a template that has space for an image. Click the Image button in the toolbar to insert an image if you need one. A nice feature here is that you can select any photo that has been automatically uploaded from your phone, but any image can be used of course.
OK, so you have a slide and it contains an image. Click the image to select it and you can now use the crop tool in the toolbar to trim it so that it only shows the part that is of interest.
It doesn't just crop though, it can apply a mask. Click the arrow next to the crop tool and select one of the many shapes that appear in the panel:
There are more editing tools and the image has a border. The colour of the border and the line thickness can be selected using the editing tools in the toolbar:
These tools mean that you can edit images within the slide show creator and you don't need to mess around with a photo editor preparing them before you start. You just add images and edit them as you go. It is much easier this way.