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Image Steganography using OpenCV in Python
• Difficulty Level : Medium
• Last Updated : 10 Jan, 2020

Image Steganography is the process of hiding secret data in some image. In this post, we will hide one image inside another and convert it into another image and then extract back both the images from the previous image.

The idea behind image-based Steganography is very simple. Images are composed of digital data (pixels), which describes what’s inside the picture, usually the colors of all the pixels. Since we know every image is made up of pixels and every pixel contains 3-values (red, green, blue).

For example, suppose we have to hide img2 in img1, where both img1 and img2 are `numpy nd` array of pixel values. The size of img2 must be less than the size of img1. We are using color images, hence both will have 3 values (red, green, blue). Each pixel value varies from 0 to 255, so each pixel value is of 1 byte or 8 bits. Let `img[i][j][l]` be the pixel value at location `(i, j)` and of channel l where i varies from 0 to width and j varies from 0 to height and l varies from 0 to 2.

Note: The quality of the new images is a little bit less than the old images.

#### Encoding

Let `img1[i][j][l]` and `img2[i][j][l]` be some pixel value of each image. Let v1 be 8 bits binary representation of `img1[i][j][l]` and v2 be 8 bits binary representation of `img2[i][j][l]`. Therefore, `v3=v1[:4]+v2[:4]`, where, v3 is the first 4 bits of v1 and v2. Then we assign `img1[i][j][l]` to v3.

Here img1 is the final image produced after encoding.

#### Decoding

Let `img[i][j][l]` be the pixel value of the image. Let v1 be 8 bits binary representation of `img[i][j][l]`. Let `v2=v1[:4]+4` random bits and `v3=v1[4:]+4` random bits. Then we assign `img1[i][j][l]` to v2 and `img2[i][j][l]` to v3.

Here img1 and img2 are the final images produced after decoding.

Implementation

Lets’ consider the images used are as follows:

Image 1

Image 2

We want to hide image2 in image1. Below is the implementation.

 `# Python program to demonstrate ` `# image steganography using OpenCV ` ` `  ` `  `import` `cv2 ` `import` `numpy as np ` `import` `random ` ` `  ` `  `# Encryption function ` `def` `encrypt(): ` `     `  `    ``# img1 and img2 are the ` `    ``# two input images ` `    ``img1 ``=` `cv2.imread(``'pic1.jpg'``) ` `    ``img2 ``=` `cv2.imread(``'pic2.jpg'``) ` `     `  `    ``for` `i ``in` `range``(img2.shape[``0``]): ` `        ``for` `j ``in` `range``(img2.shape[``1``]): ` `            ``for` `l ``in` `range``(``3``): ` `                 `  `                ``# v1 and v2 are 8-bit pixel values ` `                ``# of img1 and img2 respectively ` `                ``v1 ``=` `format``(img1[i][j][l], ``'08b'``) ` `                ``v2 ``=` `format``(img2[i][j][l], ``'08b'``) ` `                 `  `                ``# Taking 4 MSBs of each image ` `                ``v3 ``=` `v1[:``4``] ``+` `v2[:``4``]  ` `                 `  `                ``img1[i][j][l]``=` `int``(v3, ``2``) ` `                 `  `    ``cv2.imwrite(``'pic3in2.png'``, img1) ` ` `  `     `  `# Decryption function ` `def` `decrypt(): ` `     `  `    ``# Encrypted image ` `    ``img ``=` `cv2.imread(``'pic3in2.png'``)  ` `    ``width ``=` `img.shape[``0``] ` `    ``height ``=` `img.shape[``1``] ` `     `  `    ``# img1 and img2 are two blank images ` `    ``img1 ``=` `np.zeros((width, height, ``3``), np.uint8) ` `    ``img2 ``=` `np.zeros((width, height, ``3``), np.uint8) ` `     `  `    ``for` `i ``in` `range``(width): ` `        ``for` `j ``in` `range``(height): ` `            ``for` `l ``in` `range``(``3``): ` `                ``v1 ``=` `format``(img[i][j][l], ``'08b'``) ` `                ``v2 ``=` `v1[:``4``] ``+` `chr``(random.randint(``0``, ``1``)``+``48``) ``*` `4` `                ``v3 ``=` `v1[``4``:] ``+` `chr``(random.randint(``0``, ``1``)``+``48``) ``*` `4` `                 `  `                ``# Appending data to img1 and img2 ` `                ``img1[i][j][l]``=` `int``(v2, ``2``) ` `                ``img2[i][j][l]``=` `int``(v3, ``2``) ` `     `  `    ``# These are two images produced from ` `    ``# the encrypted image ` `    ``cv2.imwrite(``'pic2_re.png'``, img1) ` `    ``cv2.imwrite(``'pic3_re.png'``, img2) ` `     `  `     `  `# Driver's code ` `encrypt() ` `decrypt() `

Output:

After Encryption:

After Decryption:

Image 1

Image 2

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