1. Non-transitory, tangible, computer-readable storage media containing a program of instructions that cause a computer system running the program of instructions to elicit from a human observer ground truth data useful in automatically detecting one or more features in images by doing at least the following: presenting an image to a human observer that has a visual indicator in an image, the visual indicator indicating a location and orientation with respect to the image; asking the human observer to judge whether a particular image feature is present in the image at the location and orientation indicated by the visual indicator; receiving input from the human observer indicative of whether the particular image feature is present at the location and orientation indicated by the visual indicator; storing the input received from the human observer as part of the ground truth data; and repeating the process described above one or more times in connection with a visual indicator that has a different location or orientation with respect to the image or that uses a different image; classify multiple images paired with visual indicators into multiple classifications, each classification only having images with the same numeric, measured, image characteristic; and perform the presenting, asking, receiving, and storing steps above in connection with a predetermined number of images and their visual indicators from each of the classifications, wherein the stored ground truth data has a content that is useful in automatically detecting one or more features in other images.