28. A non-transitory computer-readable medium whose contents, when executed by a computing system, cause the computing system to perform operations comprising: retrieving an image being displayed; performing optical character recognition on the retrieved image to obtain a sequence of text; identifying an advertising message associated with at least a portion of the obtained sequence of text by at least: identifying a keyword associated with the retrieved image; determining whether the sequence of text is located in the retrieved image within a threshold number of words of the keyword associated with the image; in response to determining that the sequence of text is located in the retrieved image within the threshold number of words of the keyword associated with the retrieved image, selecting a particular advertising message as the advertising message based on (i) the sequence of text and (ii) the keyword associated with the retrieved image; and in response to determining that the sequence of text is not located in the retrieved image within the threshold number of words of the keyword associated with the retrieved image, selecting a particular advertising message as the advertising message based on the sequence of text; and providing the advertising message for display.
28. A non-transitory computer-readable medium whose contents, when executed by a computing system, cause the computing system to perform operations comprising: retrieving an image being displayed; performing optical character recognition on the retrieved image to obtain a sequence of text; identifying an advertising message associated with at least a portion of the obtained sequence of text by at least: identifying a keyword associated with the retrieved image; determining whether the sequence of text is located in the retrieved image within a threshold number of words of the keyword associated with the image; in response to determining that the sequence of text is located in the retrieved image within the threshold number of words of the keyword associated with the retrieved image, selecting a particular advertising message as the advertising message based on (i) the sequence of text and (ii) the keyword associated with the retrieved image; and in response to determining that the sequence of text is not located in the retrieved image within the threshold number of words of the keyword associated with the retrieved image, selecting a particular advertising message as the advertising message based on the sequence of text; and providing the advertising message for display. 29. The non-transitory computer-readable medium of claim 28 , wherein the advertising message is displayed on a first display device.