a simple way to check png with alpha channel reading IHDR PNG HEADER

$readPng =    fopen    ($argSourceImagePath, "rb");
$readAlp =    fread    ($readPng, 52);
            fclose    ($readPng);

if(substr(bin2hex($readAlp),50,2) == "04" || substr(bin2hex($readAlp),50,2) == "06")
echo("Png has alpha");