1. A method of securing an image displayed on an external display device and detected by an electronic device, the method comprising: generating image data associated with the detected image using the electronic device; detecting, by the electronic device, a security marker displayed by the external display device, the security marker being periodically displayed to be undetectable by a human eye that is viewing the display device; in response to detecting the security marker, modifying the image data to obscure an image portion circumscribed by a security boundary defined by the detected security marker; and generating a captured image including the obscured image portion for securing the detected image.