Download pngcrush
Create a new images/compress.bat file
for /f "tokens=*" %%x in ('dir /b *.png') do (
echo "crushing %%x"
pngcrush_1_7_58_w64.exe -brute "%%x" temp.png
move /Y temp.png "%%x"
)Put all *.png images under the images folder and run
$ compress.bat