To circumvent prevalent text-based anti-spam filters, spammers have begun embedding the advertisement text in images. Analogously, proprietary information (such as source code) may be communicated as screenshots to defeat text-based monitoring of outbound e-mail. The proposed method separates spam images from other common categories of e-mail images based on extracted overlay text and color features. No expensive OCR processing is necessary. Our method works robustly in spite of complex backgrounds, compression artifacts, and a wide variety of formats and fonts of overlaid spam text. It is also demonstrated successfully to detect screen-shots in outbound e-mail.

A technique for verifying an object hypothesis by comparing hypothesized edge patterns to detected edge patterns is presented. Positive evidence for a hypothesis is identified as those portions of the model edges that are found in the image, either as geometrical features (such as straight lines or circular arcs} or as linked edges of arbitrary shape. Occluded portions of a model edge are detected by analyzing junctions of image and model edge chains. Negative evidence is identified as those portions of the model edges that are not found and are not occluded. We describe the types of junctions that can occur between image and model edges and discuss a technique for identifying occluded regions based on these junctions. Preliminary results of these techniques are also presented.