# Quantum Image Steganography Schemes for Data Hiding: A Survey
## 1 Introduction  
Steganography defines the concept of embedding secret data into a cover message and sending it, such that only the sender and the receiver can learn the content of the embedded message. Thus, any intruder who tries to eavesdrop on the interaction will access the cover data, while the hidden message is protected from being accessed [1]. Quantum steganography, which is a combination of classical steganography [2] and quantum computing, applies the same concept of hiding data using quantum technologies and protocols. A narrower concept, quantum image steganography, involves hiding messages in images and uses quantum image representations as a cover to hide confidential data [3]. In quantum image steganography, the algorithm's success strongly depends on whether the human eye can detect the embedded segment from the cover image. More areas of evaluation need to be considered when it comes to measuring the performance of a quantum steganography scheme. Different methods of embedding quantum image representations have been adopted by researchers in recent years. One of the most common approaches is the LSBq, short for the least significant qubit approach, which is inspired by the LSB approach (least significant bit) commonly implemented in classical image steganography. The LSB method explains the process of hiding confidential data by embedding each of its bits into the least significant bits of the carrier image; LSBq, on the other hand, adopts the same concept with the focus on embedding qubits rather than bits in quantum image representations [4, 5, 6]. One of the most recent implementations for LSBq is by [PERSON] et al. [6] who focused on creating a steganography scheme using only the LSBq method to hide a grayscale image in a carrier image represented by NEQR (novel enhanced quantum image representation) [7]. [PERSON] et al. [5] also used the LSBq approach to implement quantum image steganography in an image modeled by quantum multi-wavelength image representation (QRMW) [8], allowing to hide larger scales of the secret message into the carrier image by varying its wavelengths. Furthermore, the inverted pattern approach applied the LSB method through [PERSON] et al. [9]'s approach to enhance the embedding process in a straightforward and simple execution. Another approach that aimed for a high embedding efficiency is the use of the (CAQW) (controlled alternate quantum walks) protocol for enhancing the procedure of embedding qubits into a cover image, which has shown to produce outperforming results in all areas, including resistance to data loss threats [10]. One of the challenges that researchers face when creating steganographic images is low resolution. Therefore, researchers have incorporated protocols and embedding schemes that preserve the image's quality. For example, the pixel value differencing approach achieved the goal of improving the quality of the embedding procedure as well as preserving the high-resolution state of the cover image by using the differential value between two successive pixels [11]. In addition, the image interpolation-based scheme has shown excellent embedding capacity without affecting image quality [12]. There are quantum schemes included in this paper that have shown diverse and novel approaches for quantum steganography, with some being primarily innovated for quantum applications. An example is [PERSON] et al. [13]'s new approach to quantum steganography by manipulating the characteristics of the communication channel of an entangled pair of photons. In addition, [PERSON] et al. [14] implemented quantum Hilbert scrambling in secret images and embedded them into an image by the alpha blending operation. Other researchers have developed quantum renditions of classical works to create new approaches to steganography. For example, [PERSON] et al. [15]'s use of the turtle-shell-based matrix, [PERSON] et al. [9]'s use of inverted quantum images to produce a higher image quality, [PERSON] et al.