Good for testing recognition algorithms. Computational Colour Constancy Data - A dataset oriented towards computational color constancy, but useful for computer vision in general. It includes synthetic data, camera sensor data, and over 700 images.
Most sets have a description file with names of objects in each image.
Digital Embryos - Digital embryos are novel objects which may be used to develop and test object recognition systems. They have an organic appearance. FVC2000 Fingerprint Databases - FVC2000 is the First International Competition for Fingerprint Verification Algorithms. Ratings on emotion adjectives are also available, free of charge, for research purposes. Mammography Image Databases - 100 or more images of mammograms with ground truth.