Nick Pettit offers a great bit of advice on the Treehouse blog:
Photos of your product and people using it play on the customer’s empathy in ways that colorful layouts and illustrations cannot. It helps them identify with the product and visualize themselves in the same context.
Making them span the entire width of the browser window adds to the immersion and transforms the page into a place, if you will.
Pettit provides several key pointers on using photos in homepage design and a couple of great examples. Here’s one my favorites from Harvest, which up until recently served as ReadyMadeWeb’s billing platform:
Upon reflection, it’s entirely possible that this photo, which has been in place since we signed-up for Harvest, had a big influence on my deciding to purchase the service. Picturing myself helping team members log their time made we focus on Harvest’s time tracking feature, which was already important to me, but the photo helped that idea stick.