What are the optimal dimensions/resolution for a blog banner?

I always have felt it's a best practice when a UI that allows the uploading of images in a way that significantly impacts a page, that the suggested resolution or an ideal dimension should be offered. I feel like I've seen this somewhere in Telligent but it would definitely be nice to have throughout the system... or at least some single documentation that outlines suggested dimensions for all uploaded images.

This particular question is geared towards finding out the recommended dimensions for the main image that's used as the "Group - Banner" for blog posts.

, it would be pretty cool if you had some kind of documentation around optimal image sizes, dimension, resolution, etc. for all places within Telligent where you can upload an image. e.g. a few - blog post images, blog banner, group avatars, user avatars, user banners, badges, featured items, etc. etc. Maybe something like this already exists??