Cropperjs is a slick and lightweight responsive cropping tool for images. It supports 39 options, 27 methods and 6 events. You can select an specific area of an image, and then upload the coordinates data to server-side to crop the image, or crop the image on browser-side directly. The plugin is regularly updated and has tons of potential! Making it a great fit for SmartAdmin for PHP.
Find in-depth, guidelines, tutorials and more on Cropper's Official Documentation