Visual Hunt is one of the best sources of free photography which I’ve ever come across. It has hundreds of millions (yes, hundreds of millions!) of photos, easily searchable and with very clear details of how they can be used and what (if any) attribution is required. Some 60,000 are public domain and can be used wherever and whenever, for free. If you’re writing think-pieces where your company product photo library won’t do, or if you just want some filler images for a leaflet, this is a terrific resource. Take a look.