The problem is that you probably doing it all fully on the client side.
I would advise to use HTML5 Canvas element. Please see this minimal manual:
http://www.html5canvastutorials.com/tutorials/html5-canvas-image-crop[
^].
Your solution will require a lot more, but handling the images is the key. Explaining all the aspects of such behavior would require too much time and space to fit this
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—SA
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