The strategy: fit crops to fill the box, auto scales to fit inside it, exact and square stretch, portrait currently errors and should be auto with only a height. Blur is an original smaller than the requested size, or a 1x image on a high-density screen without the 2x source, which is only offered when picture tags are on, the image was resized in the template and the original is at least one and a half times the requested size. Compression quality is a setting, judged on real images with the URL parameters l and q.