Since ProBoards upgraded the forum software, it is no longer necessary to resize large images to fit the width of the screen. However, there may be occasions when you want to reduce the image size, and you can do so with this formula, using square brackets instead of curly ones:
Note you have to calculate the correct height for your chosen width.
Here's the same image posted at full size:
The forum's dynamic resizing feature automatically reduces the width of large images to fit your screen resolution and keeps the height in the correct ratio. Specifying the image dimensions using the above formula will override this feature.