You can get the contents (bytes) from the image using the PHP function (http://php.net/manual/en/function.file-get-contents.php)
$contents = file_get_contents('http://www.google.com/images/logos/ps_logo2.png');
You can use CURL library as well... Here's an example of how you can downloadImageFromUrl with and save it in a local SaveLocation
function downloadImageFromUrl($imageLinkURL, $saveLocationPath) {
   $channel = curl_init();
   $curl_setopt($channel, CURLOPT_URL, $imageLinkURL);
   $curl_setopt($channel, CURLOPT_POST, 0);
   $curl_setopt($channel, CURLOPT_RETURNTRANSFER, 1);
   $fileBytes = curl_exec($channel); 
   curl_close($channel);
   $fileWritter = fopen($saveLocationPath, 'w');
   fwrite($fileWritter, $fileBytes);
   fclose($fileWritter); 
}
You can use this as follows:
downloadImageFromUrl("http://www.google.com/images/logos/ps_logo2.png", "/tmp/ps_logo2.png")
You can also get the same name of the image by parsing the URL as well...