Appropriate Photo Size for PowerPoint Presentation

I plan to give a PowerPoint presentation of my slide photos that I digitized. What’s the best photo size to show on a large screen? I’m using GigaPixel.

If you insert an image that is 3" x 5" @150 DPI you will be fine. It will have enough resolution if you stretch it in PowerPoint. If you expand it make sure to grab it at the corners so the change in size is proportional.