Validate that a file is a picture in PHP

If a file is uploaded to the开发者_C百科 server, is there a way using PHP, to make sure that it's actually a picture and not just a file with a .jpg or .gif extension?

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Using (part) of the GD library.

PHP: GD - Manual

array getimagesize ( string $filename [, array &$imageinfo ] )

The first element of the array will be 0 if there is no image. PHP: getimagesize

If you don't have GD installed (most of the time you will), you can read the file header as Shane mentioned.

EDIT: Actually, as Neal pointed out in the comments, the GD library is not even required to use this function. So use it.

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best way to check if file is an image

function is_image($path)
{
    $a = getimagesize($path);
    $image_type = $a[2];

    if(in_array($image_type , array(IMAGETYPE_GIF , IMAGETYPE_JPEG ,IMAGETYPE_PNG , IMAGETYPE_BMP)))
    {
        return true;
    }
    return false;
}

more: http://www.binarytides.com/php-check-if-file-is-an-image/

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The most efficient way would be to look at the beginning bytes of the file and test for 'magic number' file specifier. Here is a list of magic numbers.

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Header check is not enough for checking the validity of an image file. PHP Documentation clearly expresses that you shouldn't use getimagesize to check that a given file is a valid image. See https://www.php.net/manual/en/function.getimagesize.php

I use the following function to validate a image file:

    /**
     * Returns TRUE if $path is a valid Image File
     *
     * @param string $path
     * @return bool
     */
    public static function isImage(string $path)
    {

        if (!is_readable($path)) {
            return false;
        }

        // see https://www.php.net/manual/en/function.exif-imagetype.php for Constants
        // adjust this array to your needs
        $supported = [IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG];

        $type = exif_imagetype($path);

        // $type can be valid, but not "supported"
        if (!in_array($type, $supported)) {
            return false;
        }

        // check the image content, header check is not enough
        $image = false;
        switch ($type) {
            case IMAGETYPE_GIF:
                $image = @imagecreatefromgif($path);
                break;
            case IMAGETYPE_PNG:
                $image = @imagecreatefrompng($path);
                break;
            case IMAGETYPE_JPEG:
                $image = @imagecreatefromjpeg($path);
                break;
        }
        return (!!$image);
    }

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For the record: Now in 2013+ we can:

For max. compatibility (If you don't have GD library).
Use the always available mime-content-type ((PHP 4 >= 4.3.0, PHP 5))

$type = mime_content_type($filename);
if (strstr($type, 'image/'))
{
    echo 'is image';
}