The video walkthrough below demonstrates cropping an image from this wallpaper post:

You can draw the rectangular selector to whatever size you want and the crop function will take care of the rest. See, that was easy right? You now have a cropped image.

Go to the “File” menu and choose “Save” or “Save As” as desired to save the cropped version of the image.

Press Command + K keys to crop the picture, or go to the “Tools” menu and click the “Crop” option to complete the crop, the image will immediately crop down to the section that was drawn within the rectangular selector tool.

Draw the desired rectangle on the image to the region of the picture you wish to crop.

Now choose the “Rectangular Selection” tool, it’s usually set by default but you can double-check this by choosing it from the left-most pulldown menu of the Editor Toolbar.

Click the “Editor Toolbar” button, it’s located on the right side of the general image toolbar and looks like a toolbox or a little pencil.

Open the image file you want to crop into the Preview app in Mac OS X.

Cropping a Picture with Preview in Mac OS X The rest of the process is very simple and can be done quite fast, particularly once you learn how to use the tools and master some keyboard shortcuts. We’ve enabled it on a pair of older Macs in the Orbiting HQ with aftermarket SSDs in them, and so far we’ve had no issues-giant scary warning notwithstanding.To try this yourself, you’ll want to have an image handy that you can crop down, and just about any version of Mac OS X. Called trimforce, the utility can be executed from the OS X terminal, and it requires a reboot to start working. With today’s OS X 10.10.4 update, however, Apple has added a command line utility that can be used to enable TRIM on third-party SSDs without having to download and install anything. If you took a Mac that originally came with a spinning disk and installed an aftermarket SSD in it yourself, the operating system wouldn’t use TRIM on the disk-at least, not unless you resorted to third-party tools. The lone exception to that list has been Apple’s OS X, which-at least until today-only supported TRIM on its OEM SSDs. Pretty much every operating system in use these days supports TRIM-a special ATA command that the OS sends along to an SSD when deleting files on that SSD. Further Reading Ask Ars: “My SSD does garbage collection, so I don’t need TRIM… right?”

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