Google is your friend.
But look at the following links:
Anybody can build there own simple API's. For example:
//Queries to get user name, picture from mysql database
At the page that requested the picture, have the following code.(I've made it very long with unnecessary code to make it easily understandable).
$pic_location = file_get_contents('http://jayctech.com/pics.php?id=2');
<img src="<?=$pic_location?>" />