You can add images to your comment or answer easily by providing an external image URL (e.g.
https://patentimages.storage.googleapis.com/pages/US6097429-4.png) using the editor's add-image function.
When adding an image this way, the image is not only downloaded automatically from the given URL and stored at imgur.com, but the editor also adds the appropriate markup, which, e.g., may look like
![Image] : https://i.stack.imgur.com/c3HEkl.png to show the image in your text.
That's very convenient and an immaculate smooth workflow. No manual download and upload involved, the process is completely automatic. However, some images (e.g. technical drawings, images in patent letters, etc.) would look better when presented in a different orientation compared to the original, see the example image below which was originally retrieved from Google's patent server.
To present the image in the proper orientation, the user would have to download the image from the URL to the local computer, editing the image using software on the local computer and then upload the image to SO. That's not nearly as neat as the editor's add-image function. Therefore I suggest that the image could be rotated client (i.e. browser) side with an easy markup extension.
Proposal: I suggest to add an attribute to the markup to allow the image to be rotate 90° (counter)clockwise. Rotation could be implemented client side by adding the appropriate CSS style.