Thank you for reaching out to the Samsung community! You can lock the gallery app with the help of secure folder app. Kindly open gallery, select the image and move to secure folder.
Be sure to hit ♡ when you find an answer that works for you. For Further assistance, you can get in touch with us via Live Chat option by following- http://livechat.support.samsung.com/Customer_new/IN. You can also connect us via Samsung Members web community by following mentioned url-https://community.samsungmembers.com/en_IN#/
