将字符串的一部分转换为哈希值

有什么方法可以哈希字符串的一部分。例如，我有一个名为“ abc.jpg”的文件，我可以在“ .jpg”哈希之前加上字母吗？第一个文件是upload_form.php

<form enctype="multipart/form-data" action="upload_file.php" method="POST">
   <input type="hidden" name="MAX_FILE_SIZE" value="500"/>
   <input type="file" name="pix" size="60"/><br/>
   <input type="submit" name="submit" value="Upload"/>
</form>

第二个文件是upload_file.php

<?php
 if(!isset($_POST['submit']))
 {
   include("form_upload.php");
 }
 else
 {
  //if file is too large too upload
   if($_FILES['pix']['tmp_name']=="")
    {
     echo "<p>file is too large too upload, Please make sure the file you want to upload is smaller than 5MB</p>";
     include("form_upload.inc");
     exit();
    }
    //if the file is not jpeg format
   if(!preg_match("/^image\/jpeg$/",$_FILES['pix']['type']))
    {
     echo "<p>only jpg file is accepted !</p>";
     include("form_upload.inc");
     exit();
    }
    // if everything is ok
    else
    {
     $destination='C:\xampp\htdocs\test\my_application\picture\ '.$_FILES['pix']['name'];
     $tmp_file=$_FILES['pix']['tmp_name'];
     move_uploaded_file($tmp_file,$destination);
     echo "<p>picture was upload successfully</p>";
     echo "<p>Name :{$_FILES['pix']['name']}</p>";
     echo "<p>Size {$_FILES['pix']['size']}</p>";
     echo "<p>Type {$_FILES['pix']['type']}</p>";
     echo "<img src='picture/ {$_FILES['pix']['name']}' alt='picture'/>";
    }
 }
?>

我想将图片名称转换为md5值，但仅将名称转换为“ .jpg”。有没有办法做到这一点