Stock photography sites offer a wide variety of images for free use, including images of birthday cakes. BirthdayCakes4Free.com specializes in free birthday cake stock images.
Stock photography is a common way for photographers to build up their portfolio and gain name recognition. Most stock photography sites provide compensation to contributors. They then make revenue by selling the stock photography or providing it for free, with ads from partners and affiliates.
Many sites offer not only generic birthday cake images, but a large library of birthday cakes with specific names and messages on the cakes. This provides a low-cost option for customizing birthday cards and well-wishes to others.