19. The system as recited in claim 14 , wherein determining the legibility of the individual ones of the text components further comprises generating a gray-level histogram associated with the image and determining at least one of: a first number of a bin of the gray-level histogram; a last number of a bin of the gray level histogram; or a difference between the first bin number and the last bin number.
14. A system comprising: one or more processors; one or more computer-readable media; and one or more modules maintained on the one or more computer-readable media to be executed by the one or more processors to perform operations including: receiving a content item that includes an image; identifying one or more text components in the image; determining a legibility of individual ones of the text components by; generating a confidence level for the legibility of an individual text component based at least in part on a number of pixels that form the individual text component in the image; and comparing the confidence level with a legibility threshold, the legibility threshold based at least in part on a determined legibility of one or more images of training data used to train a classifier; classifying, based at least on the determining the legibility of the individual ones of the text components, the image as illegible; and sending a message indicating that the image has been determined to be illegible.