严格的标准：请仅通过引用传递变量

Strict Standards: Only variables should be passed by reference in please

if(isset($_FILES['image'])){
  $errors= array();
  $file_name = $_FILES['image']['name'];
  $file_size =$_FILES['image']['size'];
  $file_tmp =$_FILES['image']['tmp_name'];
  $file_type=$_FILES['image']['type'];
  $file_ext=strtolower(end(explode('.',$_FILES['image']['name'])));

  $expensions= array("jpeg","jpg","png","docx","pdf");

  if(in_array($file_ext,$expensions)=== false){
     $errors="<div align='center'><font color='red'>extension not allowed, please choose a JPEG or PNG file.</font></div>";
  }

The built-in end expects an array passed by reference. So the passed array has to be a variable.

  $var = explode('.',$_FILES['image']['name']);
  $file_ext=strtolower(end($var));

This means you must pass it a real variable and not a function returning an array