1. A method for determining compliance of content with a content policy of the online system, the method comprising: receiving a content item comprising text and one or more images; extracting a plurality of text signals from the text; extracting a plurality of image signals from the one or more images; inputting the plurality of text signals and the plurality of image signals into a two-tier classifier system by inputting the plurality of text signals into a text classifier model of a first tier of the two-tier classifier system, inputting the plurality of image signals into an image classifier model of the first tier of the two tier-classifier system, and inputting output classifications of the text classifier model and of the image classifier model into a second-tier classifier model, the second-tier classifier model outputting a confidence value expressing a likelihood of compliance with a content policy of an online system; determining, based on the confidence value, a compliance classification of the content item.