iPhotoMEASURE is a software tool that enables you to measure anything in a photo taken with your digital camera.
From their site: iPhotoMEASURE delivers an innovative dimension to accurate and efficient measurement. By simply taking a picture with your camera, you collect all the measurements you need. There is no need for a helper to hold the other end of the measuring tape or take risks on a ladder measuring out of reach areas. Bring measurements to your computer in a picture. iPhotoMEASURE software enables you to measure everything you need for quoting, evaluation and appraisal – plus – the measurements are permanently archived for reference. Above and beyond accuracy and convenience is the power of Remote Measurement provided by iPhotoMEASURE. Simply have your customers or associates e-mail you photos of the project, and save critical time and money by not having to go on-site yourself.