Usually code is
if ($_FILES['input_field_name']['type'] == 'image/jpeg') {
//some code
}
but it is not fully validating the file types(mime).
The following code will output the correct file type and avoids the security vulnerabilities of php.
$phpfileInfo = new finfo(FILEINFO_MIME_TYPE);
$PhpfileContents = file_get_contents($_FILES['name_of_input_field']['tmp_name']);
$MimeFileType = $phpfileInfo->buffer(PhpfileContents);