CFile::IsImage

static function IsImage($filename, $mime_type=false)
{
	$ext = strtolower(GetFileExtension($filename));
	if($ext <> '')
	{
		if(in_array($ext, explode(",", static::GetImageExtensions())))
		{
			if($mime_type === false || WebMimeType::isImage($mime_type))
			{
				return true;
			}
		}
	}
	return false;
}