How to Crop Images on Facebook
Facebook encourages you to upload images, but few can be cropped after you upload them to the site. Photos you post on Facebook Timelines, including your own, and in comments display at the default Facebook size and position until you click on them. Your Facebook cover image can be repositioned to crop it if it is larger than the required size, and you can edit the thumbnail of your profile picture to crop it to your liking.
Facebook Cover Image
Crop your Facebook cover image by clicking the "Change Cover" button that appears when you hover your cursor over the image. Facebook automatically resizes the width of the cover image to 851 pixels and crops the image height to 315 pixels. Select the "Reposition" option from the "Change Cover" menu and drag the image up or down to choose how it appears.
Facebook Profile Thumbnail
Facebook displays a thumbnail of your profile picture along with your name next to the posts and comments you make. Indicate the way the thumbnail is cropped when you upload a profile picture. Drag the corners of the box that appears over the image to crop it.
Use one of the free online image editors to crop other Facebook images. LunaPic and PicMonkey can open uploaded images -- with your permission -- and then save any changes.