Learn how to quickly crop images on Mac, without 3rd party software like Photoshop, by using Mac’s Preview app.
To crop an image on Mac, double click on your image to open it in Mac’s built-in Preview app. Now use your mouse to draw/drag a frame around the part of the image you want to crop out. Now hit Command + K on your keyboard to crop out your selection.
You can also go to Tool > Crop in your Preview app’s toolbar. It works the same, it’s just a bit slower.
If you close your Preview app after you made your crop, you can’t reverse your decision. The original image is now the cropped image. Preview doesn’t automatically save a new image file with your cropped image — which would’ve made sense — the original image is overwritten. It’s really dumb, but that’s how it works.
Note: while you’re inside the Preview app you can immediately regret your crop-decision by hitting CMD + Z, as you can do in most other apps. Then you’ll only have problems if you accidentally close Preview after cropping. I always make a backup copy of the original image before I start cropping, just to be safe.