how to check if a url is an image url with php?

i think that the idea is to get a content of the header url via curl

and check the headers

After calling curl_exec() to get a web page, call curl_getinfo() to get the content type string from the HTTP header

look how to do it in this link :

http://nadeausoftware.com/articles/2007/06/php_tip_how_get_web_page_content_type#IfyouareusingCURL

You can send a HEAD request to the server and then check the Content-type. This way you at least know what the server "thinks" what the type is.

You can check if a url is an image by using the getimagesize function like below.

function validImage($file) {
   $size = getimagesize($file);
   return (strtolower(substr($size['mime'], 0, 5)) == 'image' ? true : false);  
}

$image = validImage('http://www.example.com/image.jpg');
echo 'this image ' . ($image ? ' is' : ' is not') . ' an image file.';

If you want to be absolutely sure, and your PHP is enabled for remote connections, you can just use

getimagesize('url');

If it returns an array, it is an image type recognized by PHP, even if the image extension is not in the url (per your second link). You have to keep in mind that this method will make a remote connection for each request, so perhaps cache urls that you already probed in a database to lower connections.