Proper API Image Generation

<?php
//
// The first thing I did was clean up your code structure.  You had a lot of unnecessary spaces and newlines
// Right now, code readability is key!
//
function fetchInfo($playerGamertag) {
  $key = "********************************************";
  $basic = file_get_contents("http://www.bungie.net/api/reach/reachapijson.svc/player/details/nostats/" . $key . "/" . rawurlencode($playerGamertag));
  $map = file_get_contents("http://www.bungie.net/api/reach/reachapijson.svc/player/details/bymap/" . $key . "/" . rawurlencode($playerGamertag));
  $json = json_decode($basic, 1);
  $json_map = json_decode($map, 1); // There was no reason that this needed to be an object while the other was an array.
  unset($basic, $map, $key);

  $emblem = $json['Player']['ReachEmblem'];
  $colors = $emblem['change_colors'];
  $emblemUrl = sprintf("http://www.bungie.net/Stats/emblem.ashx?s=70&0=%s&1=%s&2=%s&3=%s&fi=%s&bi=%s&fl=%s&m=3",
                   $colors[0],
                       $colors[1],
                       $colors[2],
                       $colors[3],
                       $emblem['foreground_index'],
                       $emblem['background_index'],
                       ($emblem['flags'] + 1));

  foreach($json_map['StatisticsByMap'] as $stats) { // Updated to use the array instead of the object.
    if($stats['MapId'] == "-1") {
      if($stats['VariantClass'] == "1" || $stats['VariantClass'] == "2" || $stats['VariantClass'] == "3") {
        $totalkills += $stats['total_kills'];         //
        $totaldeaths += $stats['total_deaths'];       //
        $totalbetrayals += $stats['total_betrayals']; // $variable = $variable + $newvariable is the same thing as $variable += $newvariable, so I changed that.
        $totalassists += $stats['total_assists'];     //
        $mvp += $stats['total_first_place'];          //
        }
      }
    }

  $cache[] = time();
  $cache[] = $json['Player']['gamertag'];
  $cache[] = $json['Player']['service_tag'];
  $cache[] = $json['Player']['games_total'];
  $cache[] = $json['Player']['CampaignProgressSp'];
  $cache[] = $json['CurrentRankIndex'];
  $cache[] = $totalkills;
  $cache[] = $totaldeaths;
  $cache[] = $totalbetrayals;
  $cache[] = $totalassists;
  $cache[] = $mvp;
  $cache[] = $emblemUrl;

  return $cache;
  }

function generateImage($cache) {
  $sig = imagecreatefrompng("images/sig_glass.png");
  $getEmblem = file_get_contents($cache[11]);
  $sig_emblem = imagecreatefromstring($getEmblem);
  $sig_solo = imagecreatefrompng("images/solo/" . $cache[4] . ".png");
  $sig_rank = imagecreatefrompng("images/ranks/" . $cache[5] . ".png");
  $text_color = imagecolorallocate($sig, 255, 255, 255);

  imagesavealpha($sig, true); // sig_glass.png doesn't have alpha, but I'll leave this in case you update the template sometime.
  imagesavealpha($sig_solo, true);
  imagesavealpha($sig_rank, true);

  imagettftext($sig, 17, 0, 100, 26, $text_color, 'Utsaah.ttf', $cache[1]." - ".$cache[2]);                    //
  imagettftext($sig, 13, 0, 105, 47, $text_color, 'Utsaah.ttf', "Games Played: ".$cache[3]);                   //
  imagettftext($sig, 13, 0, 105, 85, $text_color, 'Utsaah.ttf', "Total Assists: ".$cache[9]);                  //
  imagettftext($sig, 13, 0, 280, 47, $text_color, 'Utsaah.ttf', "Total betrayals: ".$cache[8]);                // There's no need to put parentheses around strings containing variables, just do it like I did here
  imagettftext($sig, 13, 0, 105, 67, $text_color, 'Utsaah.ttf', "MVP ".$cache[10]." Time".(($cache[10] == 1) ? "" : "s")); //
  imagettftext($sig, 13, 0, 280, 67, $text_color, 'Utsaah.ttf', "Total Kills: ".$cache[6]);                    //
  imagettftext($sig, 13, 0, 280, 85, $text_color, 'Utsaah.ttf', "Total Deaths: ".$cache[7]);                   //

  imagecopyresampled($sig, $sig_emblem, 13, 12, 0, 0, 70, 70, imagesx($sig_emblem), imagesy($sig_emblem)); // I replaced imagecopyresized() with imagecopyresampled(), which retains a lot more quality when shrinking images
  imagecopyresampled($sig, $sig_rank, 517, 39, 0, 0, 30, 30, imagesx($sig_rank), imagesy($sig_rank));      // I also added the imagesx() and imagesy() functions, which get the width and height of a supplied image resource.
  imagecopyresampled($sig, $sig_solo, 429, 38, 0, 0, 30, 30, imagesx($sig_solo), imagesy($sig_solo));      // This makes it so that the whole source image is copied (and sized, if necessary), not just a portion of it.

  header("Content-type: image/png");
  imagepng($sig); // I told you, calling imagepng() without the string filename parameter causes it to output to the browser.
  imagedestroy($sig);
  }

$playerGamertag = @$_REQUEST['gamertag']; // This sets the gamertag from the POST array
if(!$playerGamertag) { // This checks that a gamertag was passed
  die("No gamertag supplied"); // If not, kill the script.
  } else if(strlen($playerGamertag) > 15) { // This checks that the gamertag is less than 15 characters long
  die("Invalid gamertag"); // If it is, kill the script.
  }

// A gamertag was passed that is considered "valid", so we continue.

$hash = md5($playerGamertag);           //
$cachefile = "cache/" . $hash . ".txt"; // You had these variables copied all over the place, for some reason.  You only need them once.

if(file_exists($cachefile)) {
  $file = file_get_contents($cachefile);
  $cache = explode("#|#", $file);
  unset($file);
  $timeDiff = time() - $cache[0];
  if($timeDiff > 3600) { // Timestamps are in seconds.  300 seconds is 5 minutes, that was just a demonstration from my script, you should use 1 hour, or 3600 seconds
    // The cache file is older than 1 hour
    $cache = fetchInfo($playerGamertag); // You also had this copied all over the place.  The more times you call this function, the more you'll hit the API with your key.  You were hitting it 4 times per run of this script before
    $str = implode("#|#", $cache);
    file_put_contents($cachefile, $str);
    unset($str);
    //generateImage($playerGamertag);
    } else {
    // The cache existed and was younger than 1 hour
    // Notice how we don't do anything since we already have our $cache variable populated
    }
  } else {
  // The cache didn't exist
  $cache = fetchInfo($playerGamertag);
  $str = implode("#|#", $cache);
  file_put_contents($cachefile, $str);
  unset($str);
  }

// At this point we have a variable called $cache that contains information either from the text file, or from the API (which was written to the text file)

generateImage($cache); // Now we generate our image
?>