How can I create multiple cropped Media images without re-uploading them?
Solution:


Install Crop API and Image Widget Crop modules
Configure Image Widget Crop as explained in the tutorial, for Image field situated in Structure &gt; Media types &gt; Image. The image style for this Image field should contain no effects.
There where you want to use cropped image, select the style for it (in content type, for example) that contain "Manual crop" effect and, if you need, "Crop and Scale effect" (to display square thumbnails in listings, for example).
There where you want to use full umage, select the style for it that contain no "Manual crop" effect.


How to use images:


Upload a large full image, crop manually the interesting part 
Use the same image there where you need it cropped and there where you need it full. It will be displayed differently on front.


Note: if you try to clone the Image entity (for example with Entity Clone module), it will not help because the clone Image entity and the original Image entity will apply the same crop.