Fit the whole photo
Keep the entire image. Space remains around it when the photo and slide have different proportions.
Fill the slide
Cover the frame. Some of the image is cropped, so check the edges for important details.
Let the subject decide.
Fit is helpful for group photos, artwork, documents and anything with details near the edges. Fill can work well for landscapes or a subject with space around it.
The examples above use the same sample photograph. Try both settings in the interactive demo to see the difference for all three images.
Try both layouts ↗