Crops an image inside the Worker in three ways: an aspect ratio (16:9, 1:1, 4:5, or any w:h) anchored by gravity with optional zoom into the centre, exact manual coordinates, or percentage margins from each edge. The summary reports the crop box and an equivalent CSS object-position so the same framing can be reproduced in a layout. PNG is processed in pure JavaScript; other formats are decoded by the browser, with JPEG/WebP output where available. Everything runs locally.