1. A computing device for determining relevance of a document to a text string, the document containing text and images, the text and the text string having terms, the document having a layout when the document is rendered, comprising: a memory storing computer-executable instructions implementing a component that, for each of a plurality of images contained in the document, identifies text associated with the image by extracting from the document that portion of the text that is determined to be adjacent to the image based on analysis of the layout of the document when the document is rendered; a component that, for each of the plurality of images, calculates a text score indicating relevance of the identified text associated with the image to the text string based on comparison of terms of the identified text to terms of the text string; and a component that determines relevance of the document to the text string based on the calculated the text score indicating relevance of the identified text associated with each of the plurality of the images to the text string and factoring in an image importance score for each of the plurality of images that indicates importance of the image to the document; and a processor for executing the instructions stored in the memory.