warning: pdflatex> libpng warning: iCCP: known incorrect sRGB profile

The newest libpng update (1.6.2 I believe?) has stricter rules about iCCP and will print this warning every time it finds a png that is broken. This warning can be ignored. Fixes would include:

• Downgrade to a older version of libpng
• Install imagemagick and convert all .png files with convert -strip (script below)
• Maybe even just disable this warning?

In the end this is a problem that should be fixed by the maintainer of the code.

Script that would change all .png files in the current directory:

for f in $(find . -type f -name "*.png")
do
echo "Processing $f ..."
convert $f -strip $f
done

To strip all .png files with ImageMagick, you can simply run the following command

find . -type f -name "*.png" -exec convert {} -strip {} \;

Saving the image with a lower bit depth will probably eliminate the problem altogether; since you have no real color variance and no alpha, 8-bit should look the same.

The reason is that with grayscale, you only really have 256 shades of gray with no RGB variance, and of course, no alpha.