Summary of methods to use PHP to determine whether a file is an image

To determine whether a file is an image, several methods have been found by searching for relevant information, including using the getimagesize function to obtain image information, and then judging or reading the first 2 bytes of the image. Let’s take a look at the detailed introduction below. Friends in need can refer to it.

Preface

In web design, if we need a picture, we usually get the file name of a picture. It is impossible to tell whether the file is an image file just by the file name. Some people may think that they can judge by the suffix name. Don't forget that the file suffix name can be changed at will. What's more, under Linux systems, file formats are not distinguished by suffixes. If you naively think that you can distinguish pictures by suffix names, then when an error occurs, you may not even know where the error is. For example, if an annoying person changes a text file to background.jpg and gives it to you to use, you may simply think that the image is damaged, but never expect that it is just a text file.

In order to avoid unnecessary problems, when getting a picture, you should correctly judge whether the file is really a picture file. Three judgment methods are summarized here. Friends in need can take a look together.

Method 1

Use the getimagesize function to obtain image information, and then make a judgment:

<?php # Script -- isimg.php
 
/* Author @ Huoty
 * Date @ 2015-11-24 16:59:26
 * Brief @ 
 */
 
function isImage($filename)
{
 $types = &#39;.gif|.jpeg|.png|.bmp&#39;; //定义检查的图片类型
 if(file_exists($filename))
 {
  if (($info = @getimagesize($filename))
   return 0;
   
  $ext = image_type_to_extension($info[&#39;2&#39;]);
  return stripos($types,$ext);
 }
 else
 {
  return false;
 }
}
  
if(isImage(&#39;isimg.txt&#39;)!==false)
{
 echo isImage(&#39;1.jpg&#39;);
 echo &#39;是图片&#39;;
}
else
{
 echo &#39;不是图片&#39;;
}
?>

Method 2

Read the first 2 bytes of the picture, and then determine whether it is a picture:

<?php # Script -- isimg2.php
 
/* Author @ Huoty
 * Date @ 2015-11-25 16:42:38
 * Brief @ 
 */
 
//判断上传的是不是图片 
function isImg($fileName)
{ 
 $file  = fopen($fileName, "rb"); 
 $bin  = fread($file, 2); // 只读2字节 
 
 fclose($file); 
 $strInfo = @unpack("C2chars", $bin); 
 $typeCode = intval($strInfo[&#39;chars1&#39;].$strInfo[&#39;chars2&#39;]); 
 $fileType = &#39;&#39;; 
 
 if($typeCode == 255216 /*jpg*/ || $typeCode == 7173 /*gif*/ || $typeCode == 13780 /*png*/) 
 { 
  return $typeCode; 
 }
 else
 { 
  // echo &#39;"仅允许上传jpg/jpeg/gif/png格式的图片！&#39;; 
  return false; 
 } 
} 
 
if (isImg("1.jpg"))
{
 echo "是图片";
}
else
{
 echo "不是图片";
}
?>

Method 3

The last one The first method is to use the exif_imagetype function, which is used to determine the type of an image. This method is simpler. Read the first bytes of an image and check its signature. Returns a corresponding constant if a suitable signature is found, otherwise returns FALSE. The return value is the same as index 2 in the array returned by getimagesize(), but this function is much faster.

The return value constant of this function is defined as follows:

1 IMAGETYPE_GIF
2 IMAGETYPE_JPEG
3 IMAGETYPE_PNG
4 IMAGETYPE_SWF
5 IMAGETYPE_PSD
6 IMAGETYPE_BMP
7 IMAGETYPE_TIFF_II（Intel 字节顺序）
8 IMAGETYPE_TIFF_MM（Motorola 字节顺序）
9 IMAGETYPE_JPC
10 IMAGETYPE_JP2
11 IMAGETYPE_JPX
12 IMAGETYPE_JB2
13 IMAGETYPE_SWC
14 IMAGETYPE_IFF
15 IMAGETYPE_WBMP
16 IMAGETYPE_XBM

<?php # Script -- isimg3.php
 
/* Author @ Huoty
 * Date @ 2015-11-25 16:53:04
 * Brief @ 
 */
 
$mimetype = exif_imagetype("1.jpg");
if ($mimetype == IMAGETYPE_GIF || $mimetype == IMAGETYPE_JPEG || $mimetype == IMAGETYPE_PNG || $mimetype == IMAGETYPE_BMP)
{
 echo "是图片";
}
?>

Summary

The above is all about PHP judging whether a file is an image. I hope The content of this article can be helpful to everyone in learning or using PHP. If you have any questions, you can leave a message to communicate.