1. A method comprising: receiving content data including a frame of image data comprised of plural pixels, each comprising at least one value; for each of plural pixels in said frame, determining a parameter associated with the pixel, said parameter relating to the amount the pixel value may be changed without noticeably impairing the appearance of the image data when rendered to a viewer; altering plural pixels in said frame to hide auxiliary data therein, the altering of each said pixel taking into account the parameter associated therewith, so as to yield encoding that conveys said auxiliary data without noticeably impairing the image data when rendered to the viewer; and including with the content data, but distinct from the pixels thereof, additional data that provides information about the content data; wherein said auxiliary data and said additional data cooperatively convey information about said content.