What is the best way to determine whether or not a file is an image in PHP?

Question

I have a sever which people can upload files to. The problem is that some of the filenames are mangled (dont have any extension) and so I cannot immediately determine file type.

Answer 1

You have two options here, one's simple and pre-built with some shortfalls, the other is complex and requires math.

PHP's fileinfo can be used to detect file types based on the file's actual header information. For instance, I just grabbed your gravitar:

But the actual code is this:

‰PNG


IHDR  szzô
IDATX…­—OL\UÆZÀhëT)¡    c•1T:1‘Š‘.Ú(]4†A“ÒEY˜à.................................

So, even without the file name I could detect it quite obviously. This is what the PHP Fileinfo extension will do. Most PNG and JPG files tend to have this header in them, but this is not so for every single file type.

That being said, fileinfo is dead simple to use, from the manual:

$fi = new finfo(FILEINFO_MIME,'/usr/share/file/magic');
$mime_type = $fi->buffer(file_get_contents($file));

Your other option is more complex and it depends on your own personal ambitions, you could generate a histogram and profile files based on their content.

Something like this looks like a GIF file:

And something like this looks like a TIFF file:

From there you'd need to generate a model over multiple types of files for what the histogram of each type should be, and then use that to guess. This is a good method to use for files that don't really have those "magic headers" that can be read easily. Keep in mind, you'll need to learn some math and how to model an average histogram function and match them against files.

Answer 2

exif_imagetype() might work

make sure you have exif enabled.

Answer 3

You can use exif_imagetype()

<?php
    $type =exif_imagetype($image);

where $type is a value

1. IMAGETYPE_GIF
2. IMAGETYPE_JPEG
3. IMAGETYPE_PNG
4. IMAGETYPE_SWF
5. IMAGETYPE_PSD
6. IMAGETYPE_BMP
7. IMAGETYPE_TIFF_II (intel byte order)
8. IMAGETYPE_TIFF_MM (motorola byte order)
9. IMAGETYPE_JPC
10. IMAGETYPE_JP2
11. IMAGETYPE_JPX
12. IMAGETYPE_JB2
13. IMAGETYPE_SWC
14. IMAGETYPE_IFF
15. IMAGETYPE_WBMP
16. IMAGETYPE_XBM
17. IMAGETYPE_ICO

From the manual:

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.

Answer 4

The type of the image is typically going to be able to be inferenced from the header information of the file.

Answer 5

For the first question is extension is known you could use the PHP function in_array() Documentation

Answer 6

If you need a fast solution, use imagesx() and imagesy(). There is also a fast way to check large image file dimensions, by reading just a small amount of data from the file header. Explained in more detail in the following url:

http://hungred.com/useful-information/php-fastest-image-width-height/