Core_Upload::is_image

public function is_image()
{
    $png_mimes  = array('image/x-png');
    $bmp_mimes  = array('image/bmp');
    $jpeg_mimes = array('image/jpg', 'image/jpe', 'image/jpeg', 'image/pjpeg');

    if (in_array($this->file['type'], $bmp_mimes))
    {
        $this->file['type'] = 'image/bmp';
    }

    if (in_array($this->file['type'], $png_mimes))
    {
        $this->file['type'] = 'image/png';
    }

    if (in_array($this->file['type'], $jpeg_mimes))
    {
        $this->file['type'] = 'image/jpeg';
    }

    $img_mimes = array
    (
        'image/gif',
        'image/jpeg',
        'image/png',
        'image/bmp',
    );

    return (in_array($this->file_type, $img_mimes, true)) ? true : false;
}