This study pioneers the use of amino acids for identifying pornographic images:
“Using Amino Acids of Images for Identifying Pornographic Images,” Vijay Naidu, Ajit Narayanan, and Manoranjan Mohanty, 2019 IEEE Conference on Multimedia Information Processing and Retrieval (MIPR), 2019. 
The authors, at Auckland University of Technology and the University of Aukland, New Zealand, report:
The pornographic images need to be regulated as they can have an adverse effect on the society. This paper purposes an image amino acid-based method to identify a pornographic image. The proposed method works by converting an image into biological amino acid form (e.g., to A, C, D, G, H, etc. form) and then extracting a signature from the image (which is represented in amino acid form) using biological tools. Using this method, a number of signatures are obtained from a set of few known pornographic images. These signatures are then matched against a database of images to find out the pornographic images. The matching is done using the openly available anti-virus scanner Clamscan. Here, the signatures obtained from the pornographic images are represented as signatures of viruses. The experimental result shows that the proposed method can identify a pornographic image with a high detection rate.
Many biologists who view themselves as being experts in the study of amino acids. This up and coming application of amino acids to pornographic images may be surprising to them.