How can I order a Google Image search by image's resolution in descending order (greater to lowest resolution)?
You can't. Google image search has no option to sort the results. They are always sorted by their relevance(according to Google's algorithm). Images can be seen sorted by resolution only when you search for similar images for an image.
You can filter the results by setting a resolution threshold. But you still cannot sort them.
You can. The catch is that searched images must have the same aspect ratio. To trigger such search you need to search image by image (locally uploaded or copypasted from internet).
