To crop an image in Paint, you simply grab the part of the image you want and remove the rest. On the Home tab of ribbon, click the "Select" tool, drag the mouse in the image area to select the part you want to keep, and then click "Crop" in the ribbon.
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Crop a Large Image
Cropping large images such as photos can be tricky because they may not fit on your computer screen without scrolling. You typically won't want to resize the image as you'll want to retain its resolution, especially if it's a photo. As a solution, you can view a scaled-down version of the image. On the View tab, click "Zoom Out" until the image is small enough to fit on your screen. Now you can go ahead and crop the image as needed.
Choose a Selection Tool Before Cropping
With Paint, you can crop a rectangular section of an image or, for unusual cases, a free-form section. To switch between selection tools, click the "Select" drop-down menu and then click the selection tool you want.
Use a Different Program for Cropping Images
Paint might provide everything you need for cropping images, and you already have it installed if you're running Windows. But there's also a wide range of other free programs, many of which offer a more robust set of cropping features. For example, you can try Pixlr, PicMonkey, LunaPic, or GooEdit, or even a specific cropping program called Cropp.me. You can visit the download sites for these programs to read about their features and decide what's best for you.