PHP function (conversion of @jcsrb Javascript function at https://gist.github.com/jcsrb/1081548) to output URL for social icons from google, facebook, gravatar, twitter, tumblr and instagram)

get_social_avatar.php

<?
function get_avatar_from_service($service, $userid, $size) {
    // Based on original Javascript function at https://gist.github.com/jcsrb/1081548
    // this return the url that redirects to the according user image/avatar/profile picture
    // implemented services: google profiles, facebook, gravatar, twitter, tumblr, default fallback
    // for google   	use get_avatar_from_service('google', profile-name or user-id , size-in-px )
    // for facebook 	use get_avatar_from_service('facebook', vanity url or user-id , size-in-px or size-as-word )
    // for gravatar		use get_avatar_from_service('gravatar', md5 hash email@adress, size-in-px )
    // for twitter		(via avatars.io)  use get_avatar_from_service('twitter', username, default )
    // for tumblr		use get_avatar_from_service('tumblr', blog-url, size-in-px )
    // for instagram	(via avatars.io) use get_avatar_from_service('instagram', user-id, size-in-px )
    // everything else will go to the fallback
    // google and gravatar scale the avatar to any size, others will guided to the next best version
    $url = '';
 
    switch ($service) {
 
    case "google":
        // see http://googlesystem.blogspot.com/2011/03/unedited-google-profile-pictures.html (couldn't find a better link)
        // available sizes: all, google rescales for you
        $url = "http://profiles.google.com/s2/photos/profile/" . $userid . "?sz=" . $size;
        break;
 
    case "facebook":
        // see https://developers.facebook.com/docs/reference/api/
        // available sizes: square (50x50), small (50xH) , normal (100xH), large (200xH)
        $sizeparam = '';
        if (is_numeric($size)) {
            if ($size >= 200) {
                $sizeparam = 'large';
            }
            if ($size >= 100 && $size < 200) {
                $sizeparam = 'normal';
            }
            if ($size >= 50 && $size < 100) {
                $sizeparam = 'small';
            };
            if ($size < 50) {
                $sizeparam = 'square';
            }
        } else {
            $sizeparam = $size;
        }
        $url = "https://graph.facebook.com/" . $userid . "/picture?type=" . $sizeparam;
        break;
 
    case "gravatar":
        // see http://en.gravatar.com/site/implement/images/
        // available sizes: all, gravatar rescales for you
        $url = "http://www.gravatar.com/avatar/" . $userid . "?s=" . $size;
        break;
 
    case "twitter":
        // using avatars.io following twitter retirement of api v1, see http://avatars.io/
        // retrieves default sized avatar, 48x48
 
        $url = "http://avatars.io/twitter/" . $userid;
        break;
 
    case "tumblr":
        // see http://www.tumblr.com/docs/en/api/v2#blog-avatar
        //TODO do something smarter with the ranges
        // available sizes: 16, 24, 30, 40, 48, 64, 96, 128, 512
        $sizeparam = '';
        if ($size >= 512) {
            $sizeparam = 512;
        }
        if ($size >= 128 && $size < 512) {
            $sizeparam = 128;
        }
        if ($size >= 96 && $size < 128) {
            $sizeparam = 96;
        }
        if ($size >= 64 && $size < 96) {
            $sizeparam = 64;
        }
        if ($size >= 48 && $size < 64) {
            $sizeparam = 48;
        }
        if ($size >= 40 && $size < 48) {
            $sizeparam = 40;
        }
        if ($size >= 30 && $size < 40) {
            $sizeparam = 30;
        }
        if ($size >= 24 && $size < 30) {
            $sizeparam = 24;
        }
        if ($size < 24) {
            $sizeparam = 16;
        }
 
        $url = "http://api.tumblr.com/v2/blog/" . $userid . "/avatar/" . $sizeparam;
        break;

    case "instagram":
        // using avatars.io to get instagram avatar, see http://avatars.io/
        // retrieves default sized avatar, 150x150
 
        $url = "http://avatars.io/instagram/" . $userid;
        break;
		
    default:
        // http://www.iconfinder.com/icondetails/23741/128/avatar_devil_evil_green_monster_vampire_icon
        // find your own
        $url = "http://i.imgur.com/RLiDK.png"; // 48x48
    }
 
 
    return $url;
}