如何检查文件是否为图像？

Can I check whether or not a certain file is an image? How can do this in PHP?

我可以检查某个文件是否是图像吗？怎么能用PHP做到这一点？

If the file is not an image, I want to give an alert message.

如果文件不是图像，我想给出一条警告信息。

5 个解决方案

#1

In addition to getimagesize(), you can use exif_imagetype()

除了getimagesize（）之外，你还可以使用exif_imagetype（）

exif_imagetype() reads the first bytes of an image and checks its signature.

exif_imagetype（）读取图像的第一个字节并检查其签名。

When a correct signature is found, the appropriate constant value will be returned otherwise the return value is FALSE. The return value is the same value that getimagesize() returns in index 2 but exif_imagetype() is much faster.

找到正确的签名后，将返回适当的常量值，否则返回值为FALSE。返回值与getimagesize（）在索引2中返回的值相同，但exif_imagetype（）的速度要快得多。

For both functions, FALSE is returned if the file is not determined to be an image.

对于这两个函数，如果文件未确定为图像，则返回FALSE。

#2

in PHP you can do it like following way

在PHP中你可以像下面这样做

if ((($_FILES['profile_picture']['type'] == 'image/gif') || ($_FILES['profile_picture']['type'] == 'image/jpeg') || ($_FILES['profile_picture']['type'] == 'image/png')))

in Javascript You can do it like following way

在Javascript中您可以像下面这样做

function checkFile() {
   var filename = document.getElementById("upload_file").value;
   var ext = getExt(filename);
 //  alert(filename.files[0].filesize);
  // alert(ext);
   if(ext == "gif" || ext == "jpg" || ext=="png")
      return true;
   alert("Please upload .gif, .jpg and .png files only.");
   document.getElementById("upload_file").value='';
   return false;
}

function getExt(filename) {
   var dot_pos = filename.lastIndexOf(".");
   if(dot_pos == -1)
      return "";
   return filename.substr(dot_pos+1).toLowerCase();
}

#3

In php we can use filetype ( string $filename ) and mime_content_type ( string $filename )

在php中我们可以使用filetype（string $ filename）和mime_content_type（string $ filename）

but mime_content_type ( string $filename ) is deprecated

但不推荐使用mime_content_type（string $ filename）

http://php.net/manual/en/function.filetype.php

In javascript we can use custom functions

在javascript中我们可以使用自定义函数

http://my-sliit.blogspot.in/2009/04/how-to-check-upload-file-extension.html

#4

I would do this to find out...

我会这样做才能找出......

$type =array('jpg','gif');

foreach($type as $val){

if($_FILES['filename']['type'] == 'image/$val')
{
echo "its an image file";
}
else{
echo "invalid image file"
}

#5

Better and faster way is to use exif_imagetype(). Something like that should do the work:

更好更快的方法是使用exif_imagetype（）。这样的事情应该做的工作：

$valid_formats = array(IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG);
$file_format = exif_imagetype($filename);

if(!in_array($file_format, $valid_formats))
    echo("File format is not valid");

#1