https://www.researchgate.net/profile/Rigan-Ap-Apid/publication/249767252_An_Algorithm_for_Nudity_Detection/links/5693b99108aeab58a9a2a57a/An-Algorithm-for-Nudity-Detection.pdf

In summary, the nudity detection algorithm works in the following manner:

1. Scan the image starting from the upper left corner to the lower right corner.

2. For each pixel, obtain the RGB component values.

3. Calculate the corresponding Normalized RGB and HSV values from the RGB values.

4. Determine if the pixel color satisfies the parameters for being skin established by the skin color distribution model.

5. Label each pixel as skin or non-skin.

6. Calculate the percentage of skin pixels relative to the size of the image.

7. Identify connected skin pixels to form skin regions.

8. Count the number of skin regions.

9. Identify pixels belonging to the three largest skin regions.

10. Calculate the percentage of the largest skin region relative to the image size.

11. Identify the leftmost, the uppermost, the rightmost, and the lowermost skin pixels of the three largest skin regions. Use these points as the corner points of a bounding polygon.

12. Calculate the area of the bounding polygon.

13. Count the number of skin pixels within the bounding polygon.

14. Calculate the percentage of the skin pixels within the bounding polygon relative to the area of the polygon.

15. Calculate the average intensity of the pixels inside the bounding polygon.

16. Classify an image as follows:

a. If the percentage of skin pixels relative to the image size is less than 15 percent, the image is not nude. Otherwise, go to the next step.

b. If the number of skin pixels in the largest skin region is less than 35% of the total skin count, the number of skin pixels in the second largest region is less than 30% of the total skin count and the number of skin pixels in the third largest region is less than 30 % of the total skin count, the image is not nude.

c. If the number of skin pixels in the largest skin region is less than 45% of the total skin count, the image is not nude.

d. If the total skin count is less than 30% of the total number of pixels in the image and the number of skin pixels within the bounding polygon is less than 55 percent of the size of the polygon, the image is not nude.

e. If the number of skin regions is more than 60 and the average intensity within the polygon is less than 0.25, the image is not nude.

f. Otherwise, the image is nude.