PHP Check Image Types

function checkjpeg($filename) {
    $filesize = filesize($filename);
    $fres = fopen($filename,"r");
    if ($fres == false) { return false;}
    $fstart = bin2hex(fread($fres,2));
    fseek($fres, $filesize-2);
    $fend = bin2hex(fread($fres,2));

    if ($fstart == "ffd8" && $fend == "ffd9") {
        return true;
    } else {
        return false;
    }
    fclose($fres);
}

function checkpng($filename) {
    $filesize = filesize($filename);
    $fres = fopen($filename,"r");
    if ($fres == false) { return false;}
    $fstart = bin2hex(fread($fres,8));


    if ($fstart == "89504e470d0a1a0a") {
        return true;
    } else {
        return false;
    }
    fclose($fres);
}


function checkgif($filename) {
    $filesize = filesize($filename);
    $fres = fopen($filename,"r");
    if ($fres == false) { return false;}
    $fstart = bin2hex(fread($fres,6));

    if ($fstart == "474946383961" || $fstart == "474946383761") {
        return true;
    } else {
        return false;
    }
    fclose($fres);
}