Crop workflow is a mechanism that actually takes a image and creates another one from it, applying necessary conversions and cropping.
This happens when you drag a wire or archived image over an article or a page, or when you run an appropriate option in the Upload menu on the File menu.
There are two workflows in the standard configuration:
•wf_Crop.xml: converts 'image' object (wire image, uploaded image, archived image) into editorial image.
•wf_CropImg.xml: copies "img" object (editorial image) into another editorial image (since the version 1.6).
See also
Changes in crop workflow in version 1.6