(PHP 3 >= 3.0.13, PHP 4, PHP 5)
imagepng -- Output a PNG image to either the browser or a file
Description
bool 
imagepng ( resource image [, string filename] )
     The imagepng() outputs a GD image stream
     (image) in PNG format to standard output
     (usually the browser) or, if a filename is given by the
     filename it outputs the image to the file.
     
    
     See also imagegif(), imagewbmp(),
     imagejpeg(), imagetypes().