php question checking pics format

Question

I have problem to check picture format the code:

// 0 means a successful transfer
if ($_FILES["fname"]["error"] > 0) {
    $_FILES["fname"]["name"] = "holder.jpg";        // line 3
    $imgData = $hyperlink.$_FILES["fname"]["name"]; // line 4
} else {
    $imgData = $hyperlink.$_FILES["fname"]["name"];
}

// Only accept files of jpeg format
$img = substr($imgData, 37);
$_FILES["fname"]["type"] = $img;

print "****";

print $_FILES["fname"]["type"];

//print $img;

print "****";

// only accept jpg images pjpeg is for Internet Explorer.. should be jpeg
if (!($_FILES["fname"]["type"] == "image/pjpeg") || !($_FILES["fname"]["type"== "image/jpg")) {
    print "I only accept jpg files!"; 
    exit(0);
}

It always goes to the first if statment (line 3 and 4). If I don’t upload the pictures and when it goes to if statment to check the format and it gives me I only accept jpg files. My guess it accepts it as string so that it says I only accept jpg files.

Answer 1

!($_FILES["fname"]["type"] == "image/pjpeg") || !($_FILES["fname"]["type"== "image/jpg")

is the same as

!( ($_FILES["fname"]["type"] == "image/pjpeg") && ($_FILES["fname"]["type"== "image/jpg") )

In this form you can better see that $_FILES["fname"]["type"] can never be equal with both "image/pjpeg" and "image/jpeg" so the condition is always true.

Answer 2

It would be better to check that the file is ACTUALLY a jpeg, not that its mime type on submit was a jpeg. Look into the exif_imagetype() function, or getimagesize().

<?php

  if (exif_imagetype($_FILES['fname']['tmp_name']) != IMAGETYPE_JPEG) {
    echo "Image is not a JPEG!";
    exit;
  }

If exif_imagetype isn't available, getimagesize should work:

<?php
   if ((list($width, $height, $type, $attr) = getimagesize($_FILES['fname']['tmp_name'])) !== FALSE) {
     if ($type != IMAGETYPE_JPEG) {
       echo "Image is not a JPEG!";
       exit;
     }
   }