I know I can save an image using the following method:
$input = 'http://images.websnapr.com/?size=size&key=Y64Q44QLt12u&url=http://google.com';
$output = 'google.com.jpg'; // << How to save the image with proper extension?
file_put_contents($output, file_get_contents($input));
But what if I don't know the format of the downloaded image? What if it's "png"? How can I figure out the type of target image before saving it?