What Size Should The Images Be In The Slide Show In Template 3?

Make your images as large as possible to have maximum impact in Slide Show mode.

The slide show window has a minimum format of 960×360 pixels. But you can insert images up to 1920×1080.

When you look at the slide show in standard view, any images larger than 960×360 will be cropped.  But when you click/tap on the slide show in Preview or at the Conference, it will open up as an overlay, and then it will show all images in their full size.