The present invention relates generally to signal processing of media content, e.g., audio or video content. One form of signal processing derives identifying information from media content. One claim recites a method including: upon encountering audio or video content, and using a programmed electronic processor, attempting to derive identifying information from data representing the encountered audio or video content; if a digital watermark is not obtained from the data representing the encountered audio or video content, modifying the encountered audio or video content; and then attempting to attempting to derive identifying information from data representing the modified audio or video content. Of course, other claims are provided too.