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if you have a listing with auto cropped scales (eg: scales.scale("image", scale="mini", direction="down") and you want to crop only one image of those you can't, because the autocropping direction="down" will override the saved cropped scale ...
well not only listings of course :)
for the record: i'm using https://github.com/collective/archetypes.clippingimage for automatically cropped scales as a workaround in one project.
it only supports AT (afaik) and only image access via image_ traverser (might be easy to solve), though.
as - contrary to the promise (make this package as minimally invasive as possible) in the readme - we already started to overwrite plone.app.imaging's views in this package i'd rather go and add auto-crop support there too (maybe in a separate package that can be activated by an extra eg plone.app.imagecropping[autocrop])