given the raw contents of an image file, determine the mime type and file extension

getPictureMetadata.php

<?

/**
* Given raw image data, return the file extension and MIME type of the file.
* The file extension includes the period character ('.').
*
* If the picture contents are invalid or corrupted, the values will be null.
*
* @param $picture
* @return array
* @see https://www.php.net/manual/en/function.getimagesizefromstring.php
* @see https://www.php.net/manual/en/function.getimagesize.php (for return specification)
* @see https://www.php.net/manual/en/function.image-type-to-extension.php
*/
public function getPictureMetadata($pictureContents) {
    $metadata = getimagesizefromstring($pictureContents);
    $mimeType = $metadata['mime'] ?? null;
    return [
        'extension' => $mimeType !== null ? image_type_to_extension($mimeType) : null,
        'mime' => $mimeType
    ];
}