Update privacy-shutter-replacement-image.md

Added additional note that this feature will not work on compressed frames.

Author: gerritsMSFT

windows-driver-docs-pr/stream/privacy-shutter-replacement-image.md

@@ -19,6 +19,8 @@ This feature is only implemented by cameras that have privacy shutters/kill swit
 
 Devices that want to support a custom image for image replacement must also provide a signed binary, part of their driver package that contains their replacement image.
 
+Due to image replacement overwriting the existing output buffer, this requires that the device is outputing uncompressed frames. In the case of compressed frames, such as MJPEG and JPEG, no image replacement will occur and the original image from the driver will instead be delivered.
+
 ## Implementation overview
 
 Image replacement occurs when a device sends the notification that shutter for the device is closed. If the shutter state is closed and image replacement is enabled, the camera pipeline loads the replacement image, either from a custom image provided by the camera driver or using the inbox replacement image shown here.