I am working on the ability to crop images using carrierwave and Jcrop. Its a combination of Railscasts episode 182 and 253. I have cropping working but it crops the original.
If I correctly understand the problem more simple way is to send trueSize option to the Jcrop.
<% geo = @item.image_geometry %> $('#cropbox').Jcrop({boxWidth:656,boxHeight:350,onChange:update_crop,onSelect: update_crop,aspectRatio:656/350,trueSize:[<%= "#{geo[0]}, #{geo[1]}"%>]});