I've tested Binwalk on all the example files, and the BMP and TGA samples didn't show any zlib compressed data (https://ibb.co/3vqyhcv). Can you please confirm that you have used the files from the example folder (https://github.com/x011/SecretPixel/tree/main/examples)? Regarding PNG and TIFF, this is normal because they use DEFLATE compression, which is a variant of zlib compression, to compress the image data. This is part of the PNG/TIFF specifications and is used to reduce the file size of the image. Nevertheless, I've removed TIFF compression='tiff_deflate' option for TIFF images. Thanks for the paper :)