I apologize, I wasn't very clear. I was basically looking for exactly what the mod does now—controls the size and manner in which the images display, using the ACP controls currently provided (Maximum Image Dimensions & Maximum Relative Width)—just parcelled out so images get one set of values/limits and attachments get another.
As an example, here's my quick test:
The top image was posted from a link using the [img] tag, and the bottom image is an inline attachment. I have the Max Image Dimensions set to 0x300 and Max Relative Width set to 90%. This caused them to resize to about 450x300 and 300x300 respectively (relative width didn't kick in).
I'd like to allow the [img] tag to display quite large images as long as they don't stretch the forum width, but I want to keep the attachment display sizes quite small, because people tend to post a few of them. I understand that this is a pretty esoteric requirement though.

I should probably just suck it up and get back to enjoying this mod!
