If you need a woman desperately, you can go to an authorized brothel. There are Chinese women, Malay women, Indian women and Thai women for you to choose from.
There are Vietnamese women soliciting in the bars and on the street. But there are no registered ones in the brothels. Maybe one day there will be - Vietnamese as well as Thai prostitutes in the fish-tanks in the Geylang brothels.
It is better to take photos of beautiful women on the street than to take upskirt photos.
When you take them on the street, the women don't bother you. If they don't want to be in the picture they will turn their faces away or walk quickly away from your sight.
Here are some photos of beautiful women on the street/at public places...