php如何判断一个文件是不是jpg的图片？

Question

php实现用户上传头像功能，发现有些图片是.jpg扩展名但现实异常，用图片查看软件发现图片其实是png的。这种情况如何处理，怎样在php里检测图片的真实格式？

Answer 1

<?php

$file = 'path_to_your_image.jpg';

$info = getimagesize($file);

if ($info) {
    switch ($info[2]) {
        case IMAGETYPE_JPEG:
            echo "The image is a JPEG.";
            break;
        case IMAGETYPE_PNG:
            echo "The image is a PNG.";
            break;
        case IMAGETYPE_GIF:
            echo "The image is a GIF.";
            break;
        default:
            echo "Unknown image type.";
    }
} else {
    echo "The file is not a valid image.";
}

?>

Answer 2

'image/jpeg' == mime_content_type($filepath);