This disclosure relates to advanced signal processing technology including steganographic embedding and digital watermarking. One combination disclosed in the description includes an image processing method. The method includes: obtaining an image comprising a plurality of color channels; for each color channel of the plurality of color channels, creating a grayscale version of the color channel and creating an inverted greyscale version of the color channel; analyzing the grayscale inverted version and the grayscale non-inverted version to locate image areas including an encoded signal, said analyzing yielding a plurality of image areas; generating one or more detectability measures corresponding to the encoded signal for each of the plurality of image areas; for each color channel selecting only one (1) image area as a validation point based on one or more generated detectability measures for that color channel; and generating information associated with a spatial location of each of the validation points in the image. Of course, other features and combinations are described as well.