Are they totally gone, are they red Xs now, are they a different symbol, or
if you click can you still select the "picture" but the picture itself is
just not showing?
Do you get an error message? Is it certain types of images or all? Are you
having any other issues? Can you save changes to text, add a diagram, etc?
Are you saving as a pptx or a ppt? The more detail you give us the more
likely we are to be able to help