The trouble with photos is that it is difficult (and expensive) to acquire images that meet your needs and do not look like a haphazard collection. For professional presentations, you need images that are consistent with each other and with your presentation’s style. You also may need to adapt the image to the point you want to make.
Suppose you want to craft a slide showing the ubiquity of cellphones and you have this collection of photos of people using phones in various situations:
If you don’t want to emphasize any specific venue or demographic, you need to make them more uniform. Resizing the photos to a similar size helps a little:
But the pictures have different proportions and composition – two are “head shots” and others have a wider perspective. Crop each of the images to headshots of a roughly square proportion and equal height:
Now, make a “film strip” by using picture borders and a shape for background:
Here’s another version using the bevel effect on a dark background:
(A better quality photo of the outdoorsman (Rock Hudson guy) might be needed.)
In the following examples, cropping has been used to select smaller groups or individuals from group pictures. You may want to do this simply because you need a picture of an single person or to make the image more dramatic. The smaller group emphasizes an intense discussion and is easier to “read” than the larger group.