31. An Apparatus comprising a non-transitory processor-readable medium including instructions stored on the processor-readable medium for performing at least the following: accessing information for use in determining payload information conveyed in a watermarked image, the accessed information having been produced prior to watermarking an image to produce the watermarked image, said payload information being associated with a watermark included in said watermarked image, said watermarked image and said image being arithmetically encoded by an arithmetic code, said watermark modifying at least one syntax element of said image and having watermarked said image by replacing arithmetically coded bits directly without prior arithmetic decoding and re-encoding of said image, and the accessed information including: location information that identifies a location of a set of pixels in the watermarked image, wherein the set of pixels conveys the payload information in a pixel-domain representation of the set of pixels of the watermarked image, one or more values for a feature in the pixel-domain representation of the set of pixels, wherein the one or more values for the feature indicate whether first payload information or second payload information is conveyed in the pixel-domain representation by the set of pixels, and wherein the one or more values comprise: a first value for the feature in the pixel-domain representation of the set of pixels, wherein the first value for the feature indicates that the first payload information is conveyed in the pixel-domain representation by the set of pixels; and a second value for the feature in the pixel-domain representation of the set of pixels, wherein the second value for the feature indicates that the second payload information is conveyed in the pixel-domain representation by the set of pixels; accessing the watermarked image said watermarked image having a test value for the feature based on said modified at least one syntax element; determining the a-test value for the feature of the set of pixels in the accessed watermarked image; comparing the test value with at least one of the first value and second values for the feature; and determining the payload information based on a result of the comparing of the test value.
31. An Apparatus comprising a non-transitory processor-readable medium including instructions stored on the processor-readable medium for performing at least the following: accessing information for use in determining payload information conveyed in a watermarked image, the accessed information having been produced prior to watermarking an image to produce the watermarked image, said payload information being associated with a watermark included in said watermarked image, said watermarked image and said image being arithmetically encoded by an arithmetic code, said watermark modifying at least one syntax element of said image and having watermarked said image by replacing arithmetically coded bits directly without prior arithmetic decoding and re-encoding of said image, and the accessed information including: location information that identifies a location of a set of pixels in the watermarked image, wherein the set of pixels conveys the payload information in a pixel-domain representation of the set of pixels of the watermarked image, one or more values for a feature in the pixel-domain representation of the set of pixels, wherein the one or more values for the feature indicate whether first payload information or second payload information is conveyed in the pixel-domain representation by the set of pixels, and wherein the one or more values comprise: a first value for the feature in the pixel-domain representation of the set of pixels, wherein the first value for the feature indicates that the first payload information is conveyed in the pixel-domain representation by the set of pixels; and a second value for the feature in the pixel-domain representation of the set of pixels, wherein the second value for the feature indicates that the second payload information is conveyed in the pixel-domain representation by the set of pixels; accessing the watermarked image said watermarked image having a test value for the feature based on said modified at least one syntax element; determining the a-test value for the feature of the set of pixels in the accessed watermarked image; comparing the test value with at least one of the first value and second values for the feature; and determining the payload information based on a result of the comparing of the test value. 35. The Apparatus of claim 31 wherein the location information comprises: a frame identifier that identifies the watermarked image; and a block identifier that identifies the set of pixels.