Hide the image clientside when the player says whatever the word is. If you're interested in learning to script,
Jer's guide is a good starting place. I know people have asked this exact same question in the past on these forums as well, so maybe try searching.
Otherwise if you post the code you have so far I'm sure we could guide you in the right direction. These forums are intended more for scripting help and less for script requests, so please try to keep that in mind.