Find images of cows from a large number of breeds on the Oklahoma State University Department of Animal Science website. The website maintains a list of breeds with accompanying photographs on each breed's webpage. Find anatomical images on the Online Veterinary Anatomy Museum.
The Oklahoma State University website hosts a large amount of information on domesticated cattle breeds. Amongst the information it has compiled are photographs of many, if not all, of the breeds it has cataloged.
If anatomical images are needed, the Online Veterinary Anatomy Museum contains many photographs and diagrams of cow organs and tissue. Some of their images include microscope imagery of cow cells.
Finally, for general images of cows and their ancient ancestors the aurochs, Animal Diversity Web hosts many photographs of cows in nature.