function cache_image($image_url){
	//replace with your cache directory
	$image_path = 'path/to/cache/dir/';
	//get the name of the file
	$exploded_image_url = explode("/",$image_url);
	$image_filename = end($exploded_image_url);
	$exploded_image_filename = explode(".",$image_filename);
	$extension = end($exploded_image_filename);
	//make sure its an image
	if($extension=="gif"||$extension=="jpg"||$extension=="png"){
		//get the remote image
		$image_to_fetch = file_get_contents($image_url);
		//save it
		$local_image_file  = fopen($image_path.$image_filename, 'w+');
		chmod($image_path.$image_filename,0755);
		fwrite($local_image_file, $image_to_fetch);
		fclose($local_image_file);	
	}
}

//usage
//cache_image("http://www.flickr.com/someimage.jpg");

Fetch & Save / Cache an image from a remote server using PHP

url, php, image, cache

PHP