1. A method for detecting fraud by a video surveillance system, the method comprising: receiving, by a processor in the video surveillance system, a plurality of images; converting, by the processor, the plurality of images, present at a predefined frame interval, into binary images; identifying, by the processor, a reference frame, from the binary images, having a relative white pixel count greater than a lower predefined threshold of the white pixel count; triggering, by the processor, face detection upon detecting motion within the binary images, wherein the motion is detected while the relative white pixel count either exceeds an upper predefined threshold or increases monotonically; reducing, by the processor, a Region of Interest (RoI) window within the binary images based on a highest density of white pixel count, wherein the highest density of white pixel count is determined by spatially sampling the binary images along columns; determining whether a face is detected, by the processor, within the reduced RoI window; determining whether mouth is detected within a lower half of the face, by the processor, when the face is detected within the reduced RoI window; and detecting the fraud, by the processor, when at least one of the face is not detected within the reduced RoI window and the mouth is not detected within the lower half of the detected face.