Preview editor for multiple-image posts

When you post multiple images in the same primfeed post, you get a nice grid showing previews of all of the images you're posting. But each image preview is automatically centred, with the edges of the image cropped out if it's not a square image. This means that if the focus of the image is actually outside of the centre area, the preview doesn't look as nice as it could.

It would be nice to be able to edit each image preview to drag the preview area to where you want it on the image instead of only showing the centre of the picture, for when the main focus isn't the middle of the picture.