如何確定 PHP 標頭的正確圖片內容類型？

Determining Image Content Type for PHP Header

When displaying images from outside the web root using the Header() function, users may encounter confusion regarding the specified Content-type: image/png. However, despite the fixed content type, images with various extensions (e.g., JPG, GIF) can still be displayed successfully.

To resolve this discrepancy, it is crucial to dynamically determine the correct image content type based on the file extension. The following code snippet provides a solution:

<code class="php">$filename = basename($file);
$file_extension = strtolower(substr(strrchr($filename,"."),1));

switch( $file_extension ) {
    case "gif": $ctype="image/gif"; break;
    case "png": $ctype="image/png"; break;
    case "jpeg":
    case "jpg": $ctype="image/jpeg"; break;
    case "svg": $ctype="image/svg+xml"; break;
    default:
}

header('Content-type: ' . $ctype);</code>

By utilizing this approach, the code can identify the correct content type based on the file extension and set the header accordingly. It is worth noting that the correct content type for JPG files is image/jpeg, which should be used instead of the previously confusing image/png.

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