Lossless conversion of raster images to PDF. You should use img2pdf if your priorities are (in this order):

1. always lossless: the image embedded in the PDF will always have the exact same color information for every pixel as the input
2. small: if possible, the difference in filesize between the input image and the output PDF will only be the overhead of the PDF container itself 3 fast: if possible, the input image is just pasted into the PDF document as-is without any CPU hungry re-encoding of the pixel data