Least Significant Bit 

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... images have become commonplace and nowhere are these images more prevalent than on the World Wide Web in the Internet [ 28]. Using digital images as a carrier medium is suitable for information hiding because of their insensitivity for the human visual system [11]. The vast majority of web pages are impressively sophisticated with colour images and thus Internet users browsing through the web no longer pay attention to sites containing images or to the downloading of images and data files from the Web [28]. Besides, there is a large amount of redundant bits in an image. The redundant bits of an object are those bits that can be altered but the alteration cannot be visibly detected by human eyes [13]. Based on the literature [10], [15] and [17], these existing LSB steganographic systems utilize only one LSB insertion method in concealing secret message. In addition, S-Tools and EzStego are two of the well-known steganography tools [17] that solely employ a single LSB method. However, the amalgamation of different steganography methods would enable the construction of a steganographic system that amasses the properties from various methods so that it provides a variety of algorithms for the user while increasing the difficulty of steganalysis at the same time. StegCure allows more hard codes to be added at the backend of the system by using function call to execute the method of additional algorithms. This section reviews on the least significant bit (LSB) insertion method and the significance of using GIF format in StegCure. Least significant bit insertion is a common, simple approach to embed information in a cover file [6], [17]. The LSB is the lowest order bit in a binary value. This is an important concept in computer data storage and programming that applies to the order in which data are organized, stored or transmitted [21]. Usually, three bits from each pixel can be stored to hide an image in the LSBs of each byte of a 24-bit image. Consequently, LSB requires that only half of the bits in an image be changed [27] when data can be hidden in least and second least significant bits and yet the resulting stego-image which will be displayed is indistinguishable to the cover image to the human visual system [17]. The last bit of the byte is selected as the least significant bit (as illustrated in Figure 2) because of the impact of the bit to the minimum degradation of images [12]. The last bit is also known as right-most bit, due to the convention in positional notation of writing less significant digit further to the right [7]. In bit addition (refer to Figure 3), the least significant bit has the useful property of changing rapidly if the number changes slightly. For example, if 1 (binary 00000001) is added to 3 (binary 00000011), the result will be 4 (binary 00000100) and three of the least significant bits will change (011 to 100). Basically, by modifying the insignificant bits, the cover image is typically altered in a nearly imperceptible manner thereby ensuring that any observer would be unaware of the alteration made. Employing the LSB technique for data hiding achieves both invisibility and reasonably high storage payload, a maximum of one bit per pixel (bpp) for grayscale and three bpp for Red-Green- Blue (RGB) images [31]. There are a number of steganographic tools which employ LSB insertion methods available on the web. For example, S-Tools which is invented by Andy Brown, takes a different approach by closely approximating the cover image which may mean radical palette changes. S-Tools hides the secret message within the cover file via random available bits. These available bits are determined through the use of a pseudo-random number generator. Pseudo- random is defined as random in appearance but reproducible by deterministic means, such as number generated by a series of equations. Once a pair is selected, the pixels intensities within one region are increased by a constant value while the pixels of the other region decreased by the same value [31]. The non-linear insertion makes the presence and extraction of secret messages more difficult. The image palette is taken and search for the LSB of each byte and the software then attempts to reconstruct the cover file by inserting the bits of the secret message into these LSBs [17]. Thus, S- Tools reduces the number of colours while maintaining the image quality, so that the LSB changes do not drastically change colour values. Based on the review [17], S-Tools provided the most impressive results of any steganographic package because S-Tools maintained remarkable image integrity. Another tool, which uses LSB manipulation is EzStego written by Romana Machado. Based on Figure 4, EzStego arranges the palette to reduce the occurrence of adjacent index colours that contrast too much before it inserts the message. Two adjacent colours in the sorted palette can hardly be separated [5], [22]. The modification LSB in EzStego works by twiddling the least significant bit to encode the secret message. Then, it resorts the palette by renumbering all of the colours with their original value before shifting the image. The receiver resorts the palette using the same algorithm and extracts bits by using the sorted palette. This approach works quite well in gray-scale images and may also work well in images with related colours [17]. Apparently, based on literature [13], the problem with the palette approach used with GIF images is that when one changes the least significant bit of a pixel, it can result in a completely different colour since the index to the colour palette is changed [13]. Hence, StegCure manipulated the structure of the RGB component by enhancing the basic LSB method into a colour cycle algorithm so that the stego-image will not have drastic ...