1. A method comprising: receiving a content item containing an image, the image including text; performing connected component analysis on the image to identify connected components of the image based at least in part on comparing a value of a pixel property for a particular pixel with a value of the pixel property for a neighboring pixel; classifying individual ones of the connected components of the image as text components or non-text components based at least on a text identification classifier; training a legibility classifier using one or more images of training data; determining a legibility threshold based at least in part on a determined legibility of the one or more images of the training data; determining a legibility of the individual ones of the text components by: generating, using the legibility classifier, a confidence level for the legibility of an individual text component based at least in part on one or more features of the individual text component in the image; and comparing the confidence level with the legibility threshold; classifying, based at least in part on the determining of the legibility of the individual ones of the text components, the image as illegible; and sending a message indicating that the image is illegible.