You need to combine a cropping UI with a uploader to complete this complex task. The cropping UI is responsible for displaying the cropping UI and give the cropping coordinates, and the uploader crops & resizes the image, convert it to a blob and upload it to a server.
The cropping UI is common, but the uploader is hard to find. I recommend the cropping UI ImgAreaSelect which is easy to use and this Uploader which is simple and extensible but it is not free.
