Yes, the Guides tool in Google Slides was a major help to the redesign, but so was Format options.
The Format option tool includes the option to resize images to a specific size. Try it out. In most cases, check Lock aspect ratio. In this example, I wanted the image to be 3.25 inches and 3.97. This meant I needed to crop the image. Double click on the image so that the border is black. Then change the size of the image to be the same height as the other images on the page.