Two ways, if you’re using PHP5 (or higher)
copy('http://www.google.co.in/intl/en_com/images/srpr/logo1w.png', '/tmp/file.png');
If not, use file_get_contents
//Get the file
$content = file_get_contents("http://www.google.co.in/intl/en_com/images/srpr/logo1w.png");
//Store in the filesystem.
$fp = fopen("/location/to/save/image.png", "w");
fwrite($fp, $content);
fclose($fp);
From this SO post