User talk:Dq5561

Least Significant Bit (LSB) Insertion

LSB is the simplest, earliest watermarking algorithm. For each pixel, the least significant bit is overwritten with one bit of the watermark message. For example:

"the letter A can be hidden in three pixels (assuming no compression). The original raster data for 3 pixels (9 bytes) may be (00100111 11101001 11001000) (00100111 11001000 11101001) (11001000 00100111 11101001)

The binary value for A is 10000011. Inserting the binary value for A in the three pixels would result in (00100111 11101000 11001000) (00100110 11001000 11101000) (11001000 00100111 11101001)" [4]

This takes advantage of the human visual system's inability to pick out very similar colors. Because of the large number of available colors in an uncompressed image, a substitution of adjacent colors will be undetectable.

The images below show the result of LSB insertion on various numbers of lower order bits. The same number of bits were modified for each RGB channel. For the watermark, a string of random bits were used. While the embedded message can take any form, one with a high degree of structure may create artifacts in the final image. For this reason messages should be encoded into an apparently-random string of bits (such as through MIME encoding).

Two measurements were taken, embedded capacity and PSNR. embedded capacity = (# embedded bits) / (image size)

[7] where RMSE = sqrt(MSE).