The only time I take off my mask is when I take a picture of myself.
I only remove my mask when I have my picture taken.
ーThe only time I take off my mask is when I take a picture of myself.
「マスクを外すのは写真を撮る時だけです」
to take off one's mask で「マスクを外す」
to take a picture of oneself で「自分の写真を撮る」
ーI only remove my mask when I have my picture taken.
「写真を撮ってもらう時だけマスクを外します」
to remove one's mask で「マスクを外す」
to have one's picture taken で「写真を撮ってもらう」
ご参考まで!