The three constables allegedly clicked selfies with the 45-year-old woman who was "forced to drink acid" by two men on board the Allahabad-Lucknow Ganga Gomti Express yesterday.
The purported photographs show the three constables sitting near the bed of the victim in the King George's Medical University here.
A Satish Ganesh, IG (Lucknow Zone), termed the three constables "insensitive" and said "Immediate action will be taken against them".
"We will probe the matter and check the photographs before taking any action against the three", a senior police officer said, adding they can be suspended after a departmental probe.