1. A method for determining physical characteristics of an unrestrained animal and displaying the characteristics to a user on a graphical user interface, comprising the steps of: receiving one or more captured digital images of an unrestrained animal and storing the one or more images in a digital memory device; processing at least one digital image of the unrestrained animal in a digital processor and displaying the at least one digital image on a graphical user interface; receiving a designation of the type of unrestrained animal in the at least one digital image; calibrating the animal size in the at least one digital image by accepting measurements based on user input of known size indicia for the designated animal type in the at least one image; determining measurements based on user input of the unrestrained animal in the at least one digital image for determining physical characteristics of the unrestrained animal; adjusting the measurements of the unrestrained animal based on the calibrated animal size; and displaying the at least one digital image, adjusted measurements, computed measurements, a measurement summary, and estimated measurement errors on the graphical user interface.