The aim of the invention is to provide a solution to ensure that the content sent by the IRD is the content effectively displayed on the screen.It is then proposed a system to prevent manipulation of transmitted video data comprising an Integrated Receiver Decoder (IRD) receiving audio/video data, a display device (TV), said IRD comprising means to transmit an HDMI compliant audio/video data stream toward the display device. This system comprising: means to define a variable area at a location of the image displayed on the display device, means to store reference data corresponding to video data of said area which are sent to the display device. means internal or external to the display device to extract the actual displayed video data of said area, means to send, to said IRD, test data determined from said extracted video data, means to compare said test data with said reference data, means for switching an operating mode of the system from a standard mode to a disrupted mode in case of difference resulting from this comparison.