How to Resize or Reduce Photo Size on Mac May 13, 2021, 9:30 am EDT | 2 min read If an image is too large, you can reduce its size in two ways. You can resize and reduce the resolution, or you can export it in a lower quality. Here’s how to resize or reduce photo size on Mac. You don’t need to use a third-party app to do this on your Mac. It can be done using the versatile, built-in Preview image editing app. How to Reduce Photo Size by Reducing Resolution The fastest way to reduce the photo size is by reducing the photo resolution. If a website or an application has an upper limit for a photo file size, first, try reducing the resolution.