It is not an easy task, believe me, often times I find them more likely to flutter around than willing to stay stationary for me. But when the opportunity occurs, I start shooting, the simplicity and convenience of digital photography is amazing.
Once a satisfactory photo is taken, I would attempt to identify them from materials available in the internet.
Lance Sergeant (Athyma pravara helma)
Cabbage White (Pieris canidia malayica)
Banded Demon (Notocrypta paralysos) ?? ???
There is one website that I find immensely helpful in this aspect, published as a guideline for identification of butterflies in Singapore ( http://www.geocities.com/hexaglider/ ) it appears we do share a fair amount of identical species across the causeway.