Adjusting width of attached image in markdown cell

I love the "attach image" functionality from PR #621. However, currently I need to manually adjust the size of the image before I attach it to get a proper rendering (appropriate width). If I want to change the size of the image, I need to remove the attachment, resize the image file with an editor and upload it again.

Is it possible to have some kind of way to specify the width (and/or height) of an attached image in a markdown cell?

Review PR #621 and the current attached-image behavior in markdown cells. Determine how a user could specify image width and/or height, then verify that the chosen dimensions render correctly without requiring the image to be re-uploaded.

Written by the indexing model from the issue text.