If your business has a LinkedIn, Facebook or Twitter page, you’ll need a good banner image to illustrate the page. Many companies waste the opportunity (I suspect I’d have to put my hand up here). The banner is a great opportunity to get over a lasting image. There’s space to put in a bold slogan, or just tie in neatly with any strong graphic presence you’re trying to create across all sites, including your website.
One important thing to note is that not only are the banners on the different sites quite different in size, they also get covered up by other page elements in different ways. What’s more, they need to work on mobile screens, iPad screens and large desktop screens, all of which show the image in different ways. I think I’d start by finding a business which does it well, and check out their image on a range of devices. If it works well on all of them, it could be a real time saver to reverse-engineer what they’ve done.