Open the image in Preview
Click the Markup toolbar button
Select the Rectangular Selection tool
Drag to select the area you want to keep
Go to Tools
Click Crop
Save the file
Open the image in Photos
Double-click the photo
Click Edit
Click Crop
Adjust the crop box
Click Done
Open the image in Quick Look
Press the Space bar to preview
Click the Markup icon if available
Use the selection tool to choose the area
Crop and save if supported
Open the image in Pages, Keynote, or Numbers
Select the image
Click the Format sidebar
Choose Image
Use the crop controls
Apply the crop
Use screenshot cropping
Press Shift + Command + 4
Drag to capture only the area you want
Release to save the cropped screenshot to your desktop